PVDF Spherulites Research Articles

Influence of poly(methyl methacrylate) on the structure and phase transition behavior of poly(vinylidene fluoride)

The structure and organization of poly(vinylidene fluoride) (PVDF) spherulites in blends with poly(methyl methacrylate) of high (PMMA-H) and low (PMMA-L) molecular weights, respectively, have been studied in details. It is confirmed that the addition of PMMA-H and PMMA-L have different influence on the morphologies of PVDF spherulites in several aspects, such as the spacing of ring-band α-PVDF spherulites, the kinetics of both α-PVDF crystallization and α−γ′ solid phase transition, as well as the formation of Wagon-Wheel spherulites. First, incorporation of PMMA-L enlarges the band spacing, which is associated to the increased chain mobility of crystallizable PVDF that helps to release the surface stresses of lamellae. In contrast, the low mobility of PMMA-H chains enhances the congestion at fold surfaces, which results in a vigorous twisting and thus the formation of tightened ring-band α-PVDF structure. Second, the PMMA-H reduces the crystallization rate of PVDF more severely than the PMMA-L, resulting in an extremely slow growth rate of α-PVDF spherulites in PVDF/PMMA-H sample at 160 °C, only about one-twenty-third compared to the neat PVDF. Third, the remarkably reduced α-PVDF spherulite growth rate and enhanced α−γ′ transition rate at 160 °C lead to the formation of Wagon-Wheel PVDF spherulites with inner γ′-PVDF crystals and outer γ crystals. It originates from the synchronization of slow α-PVDF growth and accelerated α−γ′ transition rate through homoepitaxy. That is, when the α−γ′ transition with exceeded rate reaches the growth front of the original α-PVDF spherulite, the transformed γ′-PVDF crystals trigger the growth of γ-PVDF crystals directly from melt with non-band feature. These results help to unravel the formation mechanism of Wagon-Wheel PVDF spherulites to be the competition of α-γ′ crystal transformation and α-spherulite radial growth rates.

Comparative Assessment of Ionic Liquid‐Based Soft Actuators Prepared by Film Casting Versus Direct Ink Writing

The growing demand for improved performance, miniaturization and more environmental friendlier devices lead to the search for better materials and processing techniques. Ionic liquid‐polymer hybrid materials allow the development of advanced materials suitable for sensors and actuators compatible with additive manufacturing techniques, allowing reduced materials waste and the fabrication of materials in a variety of shapes. In this work, ionic liquids (ILs) blended with poly(vinylidene fluoride) (PVDF) were prepared by doctor blade and direct ink writing. The selected ILs were 1‐butyl‐3‐methylimidazolium dicyanamide [Bmim][N(CN)2] and 1‐butyl‐3‐methylimidazolium thiocyanate [Bmim][SCN], based on their high conductivity value. The effects on microstructure, morphology, thermal, mechanical and electrochemical properties were evaluated, together with the actuator bending. It is shown that the printing process limits the PVDF spherulites growth, leading to lower degrees of crystallinity, which increase the ionic conductivity of the samples. The electromechanical measurements demonstrate the suitability of the developed samples to be applied as actuators, the highest displacement (7.5 mm) being obtained for [Bmim][N(CN)2]/PVDF for an applied voltage of 4 Vpp at a frequency of 0.1 Hz. The large bending (2%) is in line with the best results in the literature, confirming the suitability of printing technologies for the fabrication of high‐performance soft actuators.

In situ mussel-inspired Janus membranes using catechol and polyethyleneimine as the additives for highly efficient oil/water emulsions separation

Janus membranes (JMs) with asymmetrical wettability have been fabricated by (co)deposition of dopamine and its catechol derivatives on the hydrophobic substrates for oil/water emulsions separation, while it remains to be desired to simplify the preparation processes. Here, poly(vinylidene fluoride) membranes using catechol and polyethyleneimine as the additives were fabricated by non-solvent phase inversion on the non-woven fabric. Hydrophilic polycatechol and polyethyleneimine (PCCh-PEI) aggregates migrated on the top side of the fabricated membranes, improving their hydrophilicity. Furthermore, the hydrophobic back surface with irregular nano/micropores and lots of PVDF spherulites was gained after peeling off the supporting fabric. As a result, the as-prepared Janus membranes showed excellent emulsion separation, stability, and durability, which can potentially be used for unidirectional liquid collection with lossless transportation. This work opens a new and facile way for the fabrication of JMs with asymmetric wettability toward the versatile separation of oil/water emulsions.

Inter‐spherulitic/inner‐spherulitic localization of PBSU during crystallization of PVDF in PVDF/PBSU blend

AbstractIn this work, the miscibility effect on the localization of poly(butylene succinate) (PBSU) during the crystallization of PVDF in their blend has been investigated. After annealed at 200 °C and 240 °C, homogeneous and phase‐separated structures can be obtained respectively, which was followed by isothermal crystallization at 141 °C. In the case of 200°C, PBSU tends to enrich in inner‐spherulitic regions because of the excellent miscibility of the blend and the higher growth rate of PVDF crystals. When the specimen was annealed at 240 °C, phase separation produces PVDF and PBSU domains. Upon cooling to 141 °C, one part of PBSU is miscible with , while the other part of it remains as phase‐separated domains due to the high viscosity and slow relaxation of them. The former accounts for the distribution of PBSU in inner‐spherulitic regions. In the latter, however, phase‐separated structures depress the diffusion of PVDF during its crystallization, leading to the lower magnitude of growth rate of spherulites. Both of them contribute to the localization of PBSU in inter‐spherulitic regions. The distribution of PBSU among PVDF spherulites has been validated by long periods, pore size, and mechanical performance of the porous PVDF membranes.

Constructing a Microcapacitor Network of Carbon Nanotubes in Polymer Blends via Crystallization-Induced Phase Separation Toward High Dielectric Constant and Low Loss.

Tailoring the distribution of nanoparticles and further constructing effective microcapacitors in polymer blends are important issues for developing high-performance polymer dielectric nanocomposites. The common method to control the selective localization of nanoparticles in an immiscible polymer blend is relatively difficult and it easily results in the accumulation of nanoparticles in one component, which usually leads to a dramatic increase of the dielectric loss in the nanocomposites. In this work, a novel strategy based on step-by-step crystallization has been proposed to tailor the refined distribution and dispersion of carbon nanotubes (CNTs) in a melt-miscible blend poly(butylene succinate)/poly(vinylidene fluoride) (PBS/PVDF) through the crystallization-induced phase separation and the engineered interfacial affinity between CNTs and polymer components to acquire high dielectric constant and low dielectric loss. The results reveal that PBS is excluded along the growth front of PVDF spherulites and locates in the margin areas of PVDF spherulites during the step-by-step crystallization process. Moreover, because of the higher interfacial interaction between CNTs and PBS, CNTs are located in the PBS-rich domain, resulting in a high concentration of CNTs in the interspherulites of PVDF. Thus, the dielectric constants of the nanocomposites are greatly improved by nearly 5-24 times compared with the nanocomposites achieved by quick cooling and, simultaneously, the dielectric loss of the nanocomposites is still maintained at a low level. This work shows that the step-by-step crystallization method can be used to fabricate the nanocomposites with a synergistic increase in the dielectric performance due to the formation of a refined microcapacitor assembly. To the best of our knowledge, this is the first report to show that the dielectric constant of the nanocomposites can be greatly enhanced just through the crystallization-optimized distribution and dispersion of CNTs in immiscible polymer blends, and it possibly gives a new technical route for the fabrication of advanced dielectric composites.

Influence of fluorine interface to the crystallization of poly (vinylidene fluoride)/silicone rubber/fluororubber elastomeric tertiary blends via dynamical curing

ABSTRACTWe demonstrate the influence of fluorine interface to the crystallization of poly(vinylidene fluoride) (PVDF)/silicone rubber (SR)/fluororubber (FKM) tertiary dynamic curing blends. In contrast to PVDF/SR binary blend, the average size of PVDF spherulites turns smaller and the crystallization rate is lower in PVDF/SR/FKM tertiary blend when more fluororubber component was added into the blends at the same crystallization temperature. Incorporation of FKM does not change the crystalline form of PVDF in the blends. The resulting mechanical properties of tensile strength, flexural strength, Izod impact strength and elongation at break for PVDF/SR/FKM tertiary blends are enhanced compared with PVDF/SR binary blend.

Double equilibrium melting temperatures and zero growth temperature of PVDF in PVDF/graphene composites

Poly (vinylidene fluoride) (PVDF)/graphene composites were prepared through the melt blending method. The growths of PVDF spherulites in the composites at various temperatures were observed by means of polarized optical microscope (POM), and the melting behaviors were investigated with differential scanning calorimetry (DSC). The POM images showed that the spherulites morphology of PVDF in both pure PVDF and the composite samples presented the same well-defined Maltese-cross texture, and the radial growth rates of PVDF spherulites decreased with increasing crystallization temperature. Two equilibrium melting temperatures of PVDF were obtained and the equilibrium melting temperature of the samples crystallized above 160 °C was higher than that crystallized below 160 °C, which was attributed to the different crystal structures. Zero growth temperature of native PVDF spherulite was obtained according to the samples that crystallized above 160 °C. There is no obvious influence of adding graphene on the zero growth temperature of PVDF in the composites.

Poly(vinylidene fluoride)/cellulose nanocrystals composites: rheological, hydrophilicity, thermal and mechanical properties

Cellulose nanocrystals (CNCs) were used to improve the performance of poly(vinylidene fluoride) (PVDF), and the composite properties were characterized. The results showed that the prepared nanocomposites displayed the increases in mechanical properties. In particular, with the incorporation of 6 wt% CNCs, increases in tensile strength and dynamic storage modulus were observed. For hydrophilicity, the water contact angle decreased from 90° to 77° with the incorporation of only 3 wt% CNCs, indicating improved hydrophilicity. Addition of CNCs to PVDF also helped improve its thermal stability and crystallinity. It was suggested that CNCs played a nucleating role in the crystallization of PVDF, which was supported by the smaller size of PVDF spherulite observed from scanning electron microscopy analysis. Rheological results indicated that incorporation of CNCs also increased both melt storage modulus and shear viscosity of composites. Overall, our present work demonstrates that CNCs can provide PVDF with simultaneously improved properties.

Crystallization of poly(ethylene adipate) within γ-phase poly(vinylidene fluoride) matrix

The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy (OM), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF.

Crystallization kinetics and morphology of poly(vinylidene fluoride)/poly(ethylene adipate) blends

The miscibility, isothermal crystallization kinetics and morphology of the poly(vinylidene fluoride) (PVDF)/poly(ethylene adipate) (PEA) blends have been studied by differential scanning calorimetry (DSC), optical microscopy (OM) and scanning electron microscopy (SEM). A depression of the equilibrium melting point of PVDF was observed. From the melting point data of PVDF, a negative but quite small value of the interaction parameter χPVDF-PEA is derived using the Flory-Huggins equation, implying that PVDF shows miscibility with PEA to some extent. Nonisothermal and isothermal crystallization kinetics suggest that the crystallization rate of PVDF decreases with increasing the amount of PEA, and a contrary trend was found when PEA crystallizes with the increase of the amount of PVDF. It was further disclosed that the blend ratio and crystallization temperature affect the texture of PVDF spherulites greatly, which determines the subsequent crystallization of PEA. At high temperatures, e.g. 150 °C, the band spacing of PVDF spherulites increases with the addition of PEA content and the spherulitic structure becomes more open. In this case, spherulitic crystallization of PEA is not observed for all blend compositions. At low temperatures, e.g. 130 °C, for the PEA-rich blends, the interpenetrated structures are eventually formed by the penetration of the spherulites of PEA growing within the pre-existing PVDF spherulites.

Detailed analysis of temperature dependences of spherulite morphology and crystallite orientation of poly(vinylidene fluoride) via a combinatorial method

ABSTRACTTemperature dependences of spherulite morphology and crystal orientation of poly(vinylidene fluoride) (PVDF) were systematically investigated via a combinatorial method. The method created a temperature gradient ranging from 130 to 200 °C. Results show that the preferential orientation of the crystallites changes with the crystallization temperature. The crystallization at 169 °C gives the most highly developed crystalline state of PVDF crystalline form II (α form), in which the spherulite size is maximal, and the crystallite sizes are also the longest, about 200 nm along the b axes. Besides, the a‐axis is almost parallel to the film normal. It indicates that the crystallization rate is the highest in the b‐axis direction. The perferential orientation at higher temperatures may be attributed to the confined 2D growth of the PVDF spherulites in the thin film, whereas the spherulites grow in the 3D mode at lower temperatures. The crystallization behavior revealed in the method is consistent with the results of melt isothermal crystallization experiments. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 253–261

Poly(vinylidene fluoride)–acrylic rubber partially miscible blends: Phase behavior and its effects on the mechanical properties

A phase diagram of poly(vinylidene fluoride) (PVDF) and acrylic rubber (ACM) was plotted, and the effects of the extent of miscibility on the mechanical properties of the polymer blends were examined. A compressible, regular solution model was used to forecast the phase diagram of this blend. The model prediction, the lower critical solution temperature (LCST) over the upper critical solution temperature (UCST), was done qualitatively according to the experimentally determined phase diagram by differential scanning calorimetry (DSC), optical microscopy, and rheological analysis. These experimental methods showed that this system was miscible in ACM‐rich blends (>50% ACM) and partially miscible in PVDF‐rich blends. A wide‐angle X‐ray diffraction study revealed that PVDF/ACM blends such as neat PVDF had a characteristic α‐crystalline peak. The partially miscible blends displayed up to 350% elongation at break; this was a significant increment of this parameter compared to that of neat PVDF(20%). However, the miscible blends showed elongation of up to 1000% [again, a remarkable increase compared to chemically crosslinked ACM (220%)] and displayed excellent mechanical properties and tensile strength and a large elongation at break. For the miscible and partially miscible blends, two different mechanisms were responsible for this improvement in the mechanical properties. It was suggested that in the partially miscible blends, the rubbery depletion layer between the spherulite and the conventional rubber cavitations mechanism were responsible for the increase in the elongation at break, whereas for the miscible blends, the PVDF spherulite acted as a crosslinking junction. The stretched part of the tensile samples in the partially miscible blends showed characteristic β‐crystalline peaks in the Fourier transform infrared spectra, whereas that in the miscible blends showed α‐crystalline peaks. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1247‐1258, 2013

Confined Growth of Poly(butylene succinate) in Its Miscible Blends with Poly(vinylidene fluoride): Morphology and Growth Kinetics

The morphology and confined crystallization behavior of poly(butylene succinate) (PBS) in miscible poly(vinylidene fluoride) (PVDF)/PBS blends has been studied using differential scanning calorimetry (DSC) and optical and atomic force microscopy (OM and AFM). It was found that PBS crystal lamellae nucleated and grew confined inside the matrix of PVDF spherulites. Crystallized PBS domains grow with an ellipsoidal outline within PVDF spherulites formed at a relatively high PVDF crystallization temperature (T(c,PVDF)), while circular domains, engulfing several PVDF spherulites, are seen when growing in the PVDF spherulites created at lower T(c,PVDF). The growth kinetics of PBS confined in the PVDF matrix was investigated under various conditions. The growth rate of PBS (G(PBS)) increases with decreasing crystallization temperature and increasing PBS content under a given PVDF crystallization temperature (T(c,VDF)). For T(c,PVDF) above 145 °C, G(PBS) decreases with T(c,PVDF) for both 50:50 and 30:70 PVDF/PBS blends. However, for T(c,PVDF) below 145 °C, 50:50 and 30:70 PVDF/PBS blends exhibit the opposite G(PBS) trend; that is, G(PBS) for the 50:50 blend decreases with decreasing T(c,PVDF), while for the 30:70 PVDF/PBS blend G(PBS) increases with decreasing T(c,PVDF). It is shown that this behavior cannot be associated with the effect of crossing the boundary of smaller PVDF spherulites formed at a lower temperature. Rather, the behavior appears to be related to the interleaving growth of PBS lamellae among PVDF lamellae or between bundles of PVDF lamellae (fibrils), as in situ AFM observation shows. It is found that the interconnectedness of the molten pockets within the PVDF spherulites, which depends on the PVDF crystallization temperature, is an important factor determining the growth kinetics of PBS confined within the PVDF scaffold.

Morphologies and deformation behavior of poly(vinylidene fluoride)/poly(butylene succinate) blends with variety of blend ratios and under different preparation conditions

The morphological features and mechanical properties of PVDF/PBS blends with a variety of blend ratios and under different preparation conditions have been studied by optical and atomic force microscopy, as well as by tensile tests. It was found that, at high PVDF crystallization temperature, a small amount of PBS in the 70/30 PVDF/PBS blends has been expelled into the PVDF spherulite margin areas and interspherulitic regions due to the high diffusion ability of PBS and the slower crystal growth rate of the PVDF at high temperature. Nevertheless, the PBS affects the crystallization of PVDF significantly, which has been revealed by the increase in birefringence of PVDF spherulites of both α and γ types and the increase in band period of the α PVDF spherulites. With increasing PBS content, the increase in birefringence of PVDF spherulites and the increase in band period of the α PVDF spherulites get more evident, reflecting a more efficient influence of PBS on the crystallization of PVDF. In the PBS-rich blends, e.g., in the 40/60 and 30/70 PVDF/PBS blends, the PVDF forms isolated spherulites with large non-crystallizing PBS melt regions, which results in an interspherulitic phase separation with bigger interspherulitic PVDF areas. There is, however, PBS dispersed within the PVDF spherulites. During the crystallization of PBS at low temperature, it was found that the PBS in the interspherulitic and interaspherulitic regions growth in different manner with different growth rates. At lower PVDF crystallization temperatures, the PVDF crystallizes first and fills all the volume in regardless its content in the blends. This leads to the PBS being distributed in the interlamellar or interfibrillar regions of PVDF spherulites only. However, the growth of PBS in banded and non-banded PVDF matrix is different, reflecting the influence of pre-existing PVDF crystals on the crystallization of PBS. Tensile test shows that the deformation behavior depends remarkably on the blend ratio and the crystallization temperature of the PVDF. Such phenomena has been correlated and explained in view of the inner morphological change.

β-Phase of poly(vinylidene fluoride) formation in poly(vinylidene fluoride)/poly(methyl methacrylate) blend from solutions

The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N, N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.

Effect of Initial Polymer Concentration on the Crystallization of Poly (Vinylidene Fluoride)/Poly (Methyl Methacrylate) Blend from Solution Casting

The effect of initial polymer concentration on the crystallization of a poly (vinylidene fluoride) (PVDF)/poly (methyl methacrylate) (PMMA) blend (mass ratio=70/30) prepared by solution casting was investigated. Confirming by Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC) and wide angle X‐ray scattering (WAXD), exclusively β phase was observed in the films regardless of initial polymer concentration. Surface film morphologies examined by scanning electron microscopy (SEM) were found to be strongly dependent on the concentration. An increase of concentration resulted in a decrease of the spherulite size and a uniform distribution of PVDF spherulites owing to the fast formation of nuclei at high concentration. Correspondingly, the lateral crystal size and crystallinity of PVDF obtained from high concentration c (>10 wt.%) was less than those generated from low concentration (5–10 wt.%). This was mainly due to the reduced growth of PVDF crystals, which was caused by the increased solution viscosity and entanglement of the polymer chains with increase of concentration.

Crystallizaion and surface morphology of poly(vinylidene fluoride)/poly(methylmethacrylate) films by solution casting on different substrates

The dependence of surface structure of the poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) films by solution casting on properties of seven substrates was investigated by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). It was revealed that the polyblend films obtained by casting onto each substrate contained exclusively β phase PVDF. Higher crystallinity of the film was obtained by casting onto ceramic, polytetrafluoroethylene (PTFE), copper (Cu), stainless steel and glass substrates than that by casting onto aluminium (Al) and polypropylene (PP) substrates, depending on the degree of close lattice matching. The surface crystalline structure of PVDF was strongly affected by the wettability of substrate. The largest size of PVDF spherulitic crystal structure with about 6 μm presented in the casting film grown at the air/solution interface on glass substrate, while the smallest spherulite size with about 3 μm was generated by casting onto PTFE, stainless steel and PP substrates. It implied that the higher surface tension the substrate had, the larger PVDF spherulite grew at the air/solution interface.

Miscible Crystalline/Crystalline Polymer Blends of Poly(vinylidene fluoride) and Poly(butylene succinate-co-butylene adipate): Spherulitic Morphologies and Crystallization Kinetics

Spherulitic morphologies and overall crystallization kinetics of miscible poly(vinylidene fluoride) (PVDF)/poly(butylene succinate-co-butylene adipate) (PBSA) blends were studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). PVDF and PBSA crystallize separately in the blends. For the high-Tm component PVDF, the crystallization mechanism does not change, while both the spherulitic growth rate and the overall crystallization rate of PVDF decrease with increasing crystallization temperature and the PBSA content in the blends. Much more attention has been directed to the spherulitic morphologies and overall crystallization kinetics of the low-Tm component PBSA, which are affected not only by blend composition and crystallization temperature but also strongly by the preexisting crystals of the high-Tm component PVDF in the blends. PBSA spherulites nucleate in the matrix of the PVDF spherulites and continue to grow until impinging on ot...

Various Crystalline Morphology of Poly(butylene Succinate-co-butylene Adipate) in Its Miscible Blends with Poly(vinylidene Fluoride)

Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-butylene adipate) (PBSA) are crystalline/crystalline polymer blends with PVDF being the high-T(m) component and PBSA being the low-T(m) component, respectively. PVDF/PBSA blends are miscible as shown by the decrease of crystallization peak temperature and melting point temperature of each component with increasing the other component content and the homogeneous melt. The low-T(m) component PBSA presents various confined crystalline morphologies due to the presence of the high-T(m) component PVDF crystals by changing blend composition and crystallization conditions in the blends. There are mainly three different types of crystalline morphologies for PBSA in its miscible blends with PVDF. First, crystallization of PBSA commenced in the interspherulitic regions of the PVDF spherulites and continued to develop inside them in the case of PVDF-rich blends under two-step crystallization conditions. Second, PBSA spherulites appeared first in the left space after the complete crystallization of PVDF, contacted and penetrated the PVDF spherulites by forming interpenetrated spherulites in the case of PVDF-poor blends under two-step crystallization condition. Third, PBSA spherulites nucleated and continued to grow inside the PVDF spherulites that had already filled the whole space during the quenching process in the case of PBSA-rich blends under one-step crystallization condition. The conditions of forming the various crystalline morphologies were discussed.

Composition distributions within poly(vinylidene fluoride) spherulites as grown in blends with poly(methyl methacrylate)

AbstractUpon crystalline solidification of one component in a homogeneously molten polymer blend, composition profiles develop outside (i.e., in the rest melt) and behind (i.e., within the spherulites) the crystal growth front. The present article is devoted to the detailed verification and the interpretation of these distributions and their temporal development inside growing spherulites. To this end, the energy dispersive X‐ray emission (EDX) of suitable elements has been recorded locally resolved in a scanning electron microscope and evaluated correspondingly. The investigations were performed at the melt homogeneous blend of poly(vinylidene fluoride) (PVDF) as crystallizing and poly(methyl methacrylate) (PMMA) as steadily amorphous component. If the spherulites are not volume filling, the mean PMMA content 〈ϕPMMA〉 inside the PVDF spherulites is for all blends about 0.2 below the starting composition. ϕPMMA increases however slightly from the center of a spherulite to its border. That increase reflects the PMMA concentration in front of the spherulite surface, which increases likewise with time, and is clearly above the initial composition. There is at the spherulite surface, consequently, a remarkable jump in composition from the spherulite internal to its amorphous surroundings. It may amount up to 0.5. With volume filling spherulites, a slight variation of the composition from the center of a spherulite to its border is observed, too. This proves that also at these conditions composition profiles develop in the spherulite's surroundings. They remain however so weak that they do not inhibit crystallization even in its later stages. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 338–346, 2006