Magnetic and optical properties of poly(vinylidene difluoride)/Fe3O4 nanocomposite prepared by coprecipitation approach

Poly(vinylidene difluoride) (PVDF)/Fe₃O₄ magnetic nanocomposite was prepared by a simple coprecipitation method, and was characterized by scanning electron microscope (SEM), X‐ray diffraction (XRD), vibrating sample magnetometer (VSM), and ultraviolet visible spectroscopy (UV‐Vis). The SEM images showed that Fe₃O₄ nanoparticles were dispersed in the PVDF matrix as some aggregates with the sizes of 50 nm–2 μm, and the XRD curves showed the incorporation of the Fe₃O₄ nanoparticles in PVDF matrices and the decrease of the crystallinity of the PVDF. VSM results showed that the saturation magnetization (M_s) and remnant magnetization (M_r) of the PVDF/Fe₃O₄ nanocomposite increased with the increase of the Fe₃O₄ content, and that M_s and M_r along the parallel direction were higher than those along the perpendicular direction at the same Fe₃O₄ content. The coercive force (H_c) of the nanocomposite was independent of the Fe₃O₄ content and approximately equal along the parallel and perpendicular direction at the same Fe₃O₄ content. The optical band gap (E_g) of the PVDF/Fe₃O₄ nanocomposite was influenced by the Fe₃O₄ content, and decreased by 0.75 eV compared with that of pure PVDF when the Fe₃O₄ content was 3 wt %. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal behaviour and annealing of poly(vinylidene fluoride)

In this study, we report the melting behavior of poly(vinylidene fluoride) (PVF₂) annealed in a differential scanning calorimeter. PVF₂ annealed under isothermal conditions often shows double or triple melting endotherms depending on the annealing temperature (T_a) and the heating rate. The lower melting peak temperature increases as T_a increases. When the annealing time is varied, there is a systematic increase in the size of the lower endotherms. This suggests that a portion of the main endothermic response is due to reorganization during the scan. Annealing PVF₂ not only increases the degree of crystallinity, but also improves the crystal perfection. The ability of an annealing sample to reorganize decreases as the annealing time increases. However, an additional third melting peak appears when PVF₂ is annealed at 140°C for a sufficiently long time. The existence of this peak suggests that more than one kind of distribution of crystal perfection may occur when PVF₂ is quenched from the melt into liquid nitrogen and subsequently annealed.     

Multiple melting in blends of poly(vinylidene fluoride) with isotactic poly(ethyl methacrylate)

Multiple melting phenomena have been studied in blends of poly(vinylidene fluoride) (PVF₂) with low molar mass isotactic poly(ethyl methacrylate) (it-PEMA). In all blends, as well as in pure PVF₂, a transition (T₁) was observed prior to the main melting point (T₂). T₁ is probably connected with the melting of secondarily-crystallized material. In addition to this, a high temperature melting endotherm (T₃) was observed, which could be ascribed completely to recrystallization of PVF₂. The highest transition (T₄) was caused by melting of the σ form of PVF₂. From Hoffman-Weeks plots—T₂ vs. crystallization temperature, T_c — it could be concluded that no thermody amic depression of the melting point of PVF₂ occurred in the blends. The stabilities of PVF₂ crystallites in the various blends were derived from the slopes of Hoffman-Weeks plots and were in good agreement with lamellar thicknesses found from SAXS measurements.     

Proton exchange membranes based on poly(vinylidene fluoride) and sulfonated poly(ether ether ketone)

Blend membranes were obtained by solution casting from poly(vinylidene fluoride) (PVDF) and sulfonated poly(ether ether ketone) (SPEEK) in N,N-dimethylacetamide (DMAc). DSC and XRD were used to characterize the structure of the blend membranes. The effect of PVDF content on the membrane properties was investigated. The methanol permeability, water uptake and the swelling ratio of blend membranes decreased with the increase of PVDF content. Though the proton conductivity decreased upon the addition of PVDF, they were still comparable to that of Nafion^® 117 membrane. Higher selectivities were also found for most blend membranes in comparison with Nafion^® 117 membrane. The effect of methanol concentration on solution uptake, swelling ratio and methanol permeability of the blend membranes was also studied.     

Preparation and characterization of poly(vinylidene fluoride) nanocomposites containing multiwalled carbon nanotubes

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loadings of multiwalled carbon nanotubes (MWNT) were prepared by melt‐compounding technique. A homogeneous dispersion of MWNT throughout PVDF matrix was observed on the cryo‐fractured surfaces by scanning electron microscopy. Thermogravimetric analysis results indicated that the thermal stability of neat PVDF was improved with the incorporation of MWNT. Dynamic mechanical analysis showed a significant improvement in the storage modulus over a temperature range from ?125 to 75°C with the addition of MWNT. The melt‐rheological studies illustrated that incorporating MWNT into PVDF matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), loss modulus (G″), and lower loss factor (tan δ) than those of neat PVDF. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

聚偏氟乙烯-b-聚乙烯基吡咯烷酮嵌段共聚物的制备和结构

以C₆F₁₃I为链转移剂,通过碘转移乳液聚合制得碘封端的聚偏氟乙烯（PVDF-I）,再以PVDF-I为大分子链转移剂进行N-乙烯基吡咯烷酮碘转移溶液聚合,得到聚偏氟乙烯-b-聚乙烯基吡咯烷酮（PVDF-b-PVP）两亲性嵌段共聚物;采用NMR、IR、XRD、DSC和AFM等对PVDF-b-PVP嵌段共聚物的分子和相态结构进行了表征。发现PVP能有效嵌入PVDF与末端碘之间,PVDF嵌段PVP后,PVDF分子链的有序度明显降低,产生γ晶型PVDF,同时结晶温度和结晶度降低。PVDF-b-PVP嵌段共聚物表现微相分离结构,相分离尺寸约20 nm,其亲水性也优于PVDF均聚物。     

Spatially‐confined crystallization of poly(vinylidene fluoride)

Nanometre‐sized poly(vinylidene fluoride) (PVDF) particle domains in a confined space were obtained by blending PVDF with excess poly(methyl methacrylate) (PMMA). When these particles were small enough they showed β‐form structure, which was different from the structure of bigger particles or PVDF bulk. However, the β‐form was thermodynamically metastable because it could eventually be transformed to a more stable phase by annealing at a certain temperature. Larger particle domains were of identical phase to the bulk, indicating that small size favours the formation of the β‐form. © 2000 Society of Chemical Industry     

Compatibility of poly(vinylidene fluoride) (PVDF)/polyamide 12 (PA12) blends

Poly(vinylidene fluoride) (PVDF)/polyamide 12 (PA12) blends showed new peaks in XRD profile with increasing PA12 and the crystallinity of PA12 significantly decreased with the addition of PVDF. PVDF showed three relaxation regions at about −40, 40, and 100°C, respectively, and glass transition temperature (T_g ) of PA12 increased in blends (10.8→30.14°C) and α‐relaxation of PVDF decreased from 100.26 to 86.46°C. Complex viscosities (η*) vs. composition curve showed a great positive deviation in PVDF‐rich and a small negative deviation in PA12‐rich blends. The N—H and C=O stretching band of PA12 shifted slightly toward higher wavelength, and from curve‐fitted data the area of hydrogen‐bonded C=O stretching bands of PA12 decreased with the addition of PVDF, especially in the 30/70 blend, implying the existence of interactions between the β‐hydrogen atom of PVDF and amide carbonyl group of PA12 in the blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1374–1380, 2000     

Crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate)/poly(vinyl pyrrolidone) ternary blends

Ternary blends composed of matrix polymer poly(vinylidene fluoride) (PVDF) with different proportions of poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP) blends were prepared by melt mixing. The miscibility, crystallization behavior, mechanical properties and hydrophilicity of the ternary blends have been investigated. The high compatibility of PVDF/PMMA/PVP ternary blends is induced by strong interactions between the carbonyl groups of the PMMA/PVP blend and the CF₂ or CH₂ group of PVDF. According to the Fourier transform infrared and wide‐angle X‐ray difffraction analyses, the introduction of PMMA does not change the crystalline state (i.e. α phase) of PVDF. By contrast, the addition of PVP in the blends favors the transformation of the crystalline state of PVDF from non‐polar α to polar β phase. Moreover, the crystallinity of the PVDF/PMMA/PVP ternary blends also decreases compared with neat PVDF. Through mechanical analysis, the elongation at break of the blends significantly increases to more than six times that of neat PVDF. This confirms that the addition of the PMMA/PVP blend enhances the toughness of PVDF. Besides, the hydrophilicity of PVDF is remarkably improved by blending with PMMA/PVP; in particular when the content of PVP reaches 30 wt%, the water contact angle displays its lowest value which decreased from 91.4° to 51.0°. Copyright © 2011 Society of Chemical Industry     

Morphological and infra-red studies on highly oriented poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Highly oriented melt drawn films of poly(vinylidene fluoride) (PVDF) and blends of poly(vinylidene fluoride) and poly(methyl methacrylate) (PMMA) have been studied by transmission electron microscopy, electron diffraction and infra-red spectroscopy. Infra-red spectra show the second moment of the orientation function for PVDF samples to be greater than 0.94. Using such a sample, the transition dipole directions relative to the chain axis have been calculated. Electron microscopic studies of the PVDF/PMMA blends show a transformation for pure PVDF from a lamellar morphology to a mixture of lamellar and needle-like crystals for the 80/20 blend. The 60/40 blend shows a pure needle-like morphology. The β phase content for this blend is dependent upon the composition and thermal history. An increase in the β phase content is observed with the addition of PMMA. After annealing at 110°C, the 50/50 blend shows a lamellar β phase morphology. A significant increase in the segmental orientation of PVDF is also observed.     

FTIR-microspectroscopy and DSC studies of poly(vinylidene fluoride)

Poly(vinylidene fluoride) (PVDF) samples, obtained by casting from tetrahydrofuran solutions and submitted to various thermal treatments, have been examined by Fourier transform–infrared microspectroscopy (FTIR-M) and differential scanning calorimetry (DSC). This kind of analysis allowed us to examine microdomains of samples with different morphological characteristics and to obtain an indication of the polymorphism of PVDF. In some cases the simultaneous presence of two or three forms has been evidenced thanks to the comparison of FTIR-M spectra and DSC traces. Vibrational spectra of single crystalline forms can be recorded by FTIR-M on phase homogeneous microdomains.     

Morphology and melting behaviour of poly(vinylidene fluoride) crystallized from the melt

The influence of crystallization temperature on the melting behaviour and the morphology of poly(vinylidene fluoride) (PVF₂) has been investigated. The DSC endotherms of PVF₂ crystallized from the melt show at least two peaks. The peak areas depend on the thermal history of the samples and the heating scan rate. The area of the first peak was found to increase as the crystallization temperature or the scan rate increased. The double peak configuration was attributed to a melting–recrystallization process. Electron microscopy supports these results, for which only one type of lamella was found in the spherulitic structure.     

Investigation on crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate)/poly(vinyl pyrrolidone) ternary blends by solution casting

Ternary blends composed of matrix polymer poly(vinylidene fluoride) (PVDF) with different proportions of poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP) blends were prepared by solution casting. The crystallization behavior and hydrophilicity of ternary blends were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and contact angle test. According to morphological analysis, the surface was full of typical spherulitic structure of PVDF and the average diameter was in the order of 3 μm. The samples presented predominantly β phase of PVDF by solution casting. It indicated that the size of surface spherulites and crystalline phase had little change with the PMMA or PVP addition. Moreover, FTIR demonstrated special interactions among the ternary polymers, which led to the shift of the carbonyl stretching absorption band of PVP. On the other hand, the melting, crystallization temperature, and crystallinity of the blends had a little change compared with the neat PVDF in the first heating process. Except for the content of PVP containing 30 wt %, the crystallinity of PVDF decreased remarkably from 64% to 33% and the value of t_1/2 was not obtained. Besides, the hydrophilicity of PVDF was remarkably improved by blending with PMMA/PVP, especially when the content of PVP reached 30 wt %, the water contact angle displayed the lowest value which decreased from 98.8° to 51.0°. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structure,properties, and phase transitions of melt‐spun poly(vinylidene fluoride) fibers

Three different experimental techniques were used to study structural phase transitions in melt‐spun poly(vinylidene fluoride) fibers, which were produced with different process parameters and processed in the draw‐winding process at different temperatures and draw ratios. The fibers are examined with the help of wide‐angle X‐ray diffraction at elevated temperatures, differential scanning calorimetry with stochastic temperature modulation, and dynamic mechanical analysis. An oriented mesophase and deformed crystal structures can be observed in all fibers and assigned to the mechanical stress occurring in the processes. Furthermore, several phase transitions during melting and two mechanical relaxation processes could be detected. The observed transitions affect the crystal geometry, the orientation distribution, anisotropic thermal expansion, and the mechanic response of the fiber samples. The relaxation processes can be related with an increasing amount of crystalline β‐phase in fibers drawn at different temperatures. The detailed information about phase transitions and the related temperatures are used to produce fibers with an extended amount of β‐phase crystallites, which are responsible for piezoelectric properties of the material. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

High dielectric constant composites based on metallophthalocyanine oligomer and poly(vinylidene fluoride-trifluoroethylene) copolymer

Using a solution casting method, a high dielectric constant composite based on a copper-phthalocyanine (CuPc) oligomer and a poly(vinylidene fluoride-trifluoroethylene) copolymer is developed. The experimental data show that the low field dielectric constant of the composites (with 55 wt % CuPc) can reach 1000 and the loss is ∼0.5 at room temperature and 100 Hz. Because of the long-range electron delocalization in CuPc, which results in a strong space charge response of the composite to the external field, there is a strong frequency dispersion of the dielectric properties. In addition, the dielectric properties exhibit a nonlinear behavior with electric field. At a field of 10 kV/cm, the dielectric constant at 10 Hz reaches 4500; meanwhile the dielectric loss is also high. One of the unique attributes of the composite is its mechanical properties that remain very much the same as those of the polymer matrix. Even for a composite with 55 wt % CuPc (the volume fraction of CuPc in the composite is also in the similar range), the composite film is still flexible, with a Young's modulus of 1.2 GPa at room temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 70–75, 2001     

Controlled grafting from poly(vinylidene fluoride) microfiltration membranes via reverse atom transfer radical polymerization and antifouling properties

A reverse atom transfer radical polymerization (RATRP) with benzoyl peroxide (BPO)/CuCl/2,2-bipyridine (Bpy) was applied onto grafting of poly(methyl methacrylate) (PMMA) and poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) from poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane surfaces, including the pore surfaces. The introduction of peroxide and hydroperoxide groups onto the PVDF membranes was achieved by ultraviolet (UV) irradiation in nitrogen, followed by air exposure. RATRP from UV pretreated hydrophobic PVDF membranes was then performed for attaching well-defined homopolymer. The chemical composition of the modified PVDF membrane surfaces was characterized by attenuated total reflectance (ATR) FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF and the PMMA grafted PVDF membranes were measured using micro-image analysis and process software. With increase of graft concentration, the pore size of the modified membranes decreased and became uniform. Kinetic studies of homogeneous (in toluene solution) system revealed a linear increase in molecular weight with the reaction time and narrow molecular weight distribution, indicating that the chain growth from the membrane surface was a “controlled” or “living” grafting process. The introduction of the well-defined PMMA on the PVDF membrane gave rise to hydrophilicity. Protein adsorption and protein solution permeation experiments revealed that the UV pretreated hydrophobic PVDF membrane subjected to surface-initiated RATRP of methyl methacrylate (MMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) exhibited good antifouling property.     

Hydrophilic modification of poly(vinylidene fluoride) membrane with poly(vinyl pyrrolidone) via a cross‐linking reaction

A highly hydrophilic hollow fiber poly(vinylidene fluoride) (PVDF) membrane [PVDF‐cl‐poly(vinyl pyrrolidone) (PVP) membrane] was prepared by a cross‐linking reaction with the hydrophilic PVP, which was immobilized firmly on the outer surface and cross‐section of the PVDF hollow fiber membrane via a simple immersion process. The cross‐linking between PVDF and PVP was firstly verified via nuclear magnetic resonance measurement on PVP solution after cross‐linking. The hydrophilic stability of the modified PVDF membrane was evaluated by measuring the pure water flux after different times of immersion and drying. The anti‐fouling properties were estimated by cyclic filtration of protein solution. When the cross‐linking time was as long as 6 hr and the PVP content reached 5 wt %, the pure water flux (J_v) was constant as ～ 600 L m^?2 hr^?1. The hydrophilicity of the PVDF‐cl‐PVP membrane was significantly enhanced and exhibited a good stability. The PVDF‐cl‐PVP membrane showed an excellent anti‐protein‐fouling performance during the cyclic filtration of bovine serum albumin solution. Therefore, a highly hydrophilic and anti‐protein‐fouling PVDF hollow fiber membrane with a long‐term stability can be prepared by a simple and economical cross‐linking process with PVP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Miscibility of C60‐containing poly(methyl methacrylate)/poly(vinylidene fluoride) blends

The miscibility of C₆₀‐containing poly(methyl methacrylate) (PMMA‐C₆₀) with poly(vinylidene fluoride) (PVDF) was studied. Two PMMA‐C₆₀ samples containing 2.6 and 7.4 wt % C₆₀ were found to be miscible with PVDF based on single glass transition temperature criterion and melting point depression of PVDF. However, the interaction parameters of the two blend systems are less negative than that of the PMMA/PVDF blend system, showing that the incorporation of C₆₀ reduces the ability of carbonyl groups of PMMA to interact with PVDF. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1393–1396, 2000     

Spectroscopic study of the electric field induced microstructural changes in poly(vinylidene fluoride)

Infra-red spectra (4000-400 cm^?1) have been obtained for poly(vinylidene fluoride) films in the presence of high electric fields up to 2.6 MV cm^?1 in strength. Both band intensity and polarization studies have revealed that dipolar re-orientation can be correlated with the macroscopic electric effect. The frequency shift as a function of field strength for the β phase bands can be attributed to the non-equivalent reorientation behaviour of the bands in the unit cell. However, the change in the frequency of the α bands shifted irreversibly with the applied electric field. These changes cannot be attributed to reorientation behaviour alone.     

Formation of multilayer poly(acrylic acid)/poly(vinylidene fluoride) composite membranes for pervaporation

Dual‐ and multilayer composite membranes, consisting of poly(acrylic acid) (PAA) and poly(vinylidene fluoride) (PVDF), were synthesized by the plasma‐induced polymerization technique. The dual‐layer membrane had a dense PAA layer grafted onto a microporous PVDF substrate, whereas in the multilayer membranes, the grafted PAA and the PVDF layers were arranged in an alternating sequence (e.g., PAA/PVDF/PAA and PAA/PVDF/PAA/PVDF/PAA). These membranes were used in a pervaporation process to separate ethanol–water solutions. For the dual‐layer membranes, the results indicated that the separation factor increased and the permeation flux decreased with increasing amounts of grafted PAA. For the case of grafting yield < 0.6 mg/cm², the composite membrane demonstrated poor separation. As the grafting yield reached 0.85 mg/cm², a sharp increase of the separation factor was observed. For the multilayer membranes, the pervaporation performances were very good, with high separation factors (on the order of 100) and reasonable permeation fluxes over a wide ethanol concentration range. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2266–2274, 2004