Crystallization behavior of poly (vinylidene fluoride)/multi-walled carbon nanotubes nanocomposites

The non-isothermal and isothermal crystallization of poly (vinylidene fluoride) (PVDF)/multiple-walled carbon nanotubes (MWNTs) composites containing pristine (MWNT1) and carboxyl group (–COOH) functionalized MWNT (MWNT2) were investigated. The effects of MWNT on the crystallization behavior of PVDF were dependent on the dispersion state of MWNT. Pristine MWNT could increase the nucleation due to better dispersion, and thus, PVDF/MWNT1 composites exhibited higher crystallization peak temperatures (T _cps) and crystallinities (X _cs) compared with PVDF/MWNT2 composites. Meanwhile, the formation of MWNT network confined the growth of crystals. For the isothermal crystallization, MWNT acted as nucleating agents, and the crystallization rate constant k was increased with the addition of MWNT. Besides, the half crystallization time, t _0.5, was remarkably shortened with the increase of MWNT content, especially for the pristine MWNT.     

Crystal form and phase structure of poly(vinylidene fluoride)/polyamide 11/clay nanocomposites by high-shear processing

Polyamide 11 (PA11)/clay, Poly(vinylidene fluoride) (PVDF)/clay and PVDF/PA11/clay nanocomposites were prepared by melt processing using a high shear extruder. Two types of organoclay with different modified alkyl tails and different polarities were used for PA11 and PVDF nanocomposites. PA11 nanocomposites derived from an organoclay having one alkyl tail show a well-exfoliated morphology but no crystal form transformation, whereas those derived from an organoclay having two alkyl tails give a little worse clay dispersion with the clear alpha to gamma crystal form transition with the addition of the clay. In contrast, the PVDF composites derived from the two organoclays result in a poor dispersion. In addition, PVDF/PA11 blend nanocomposites with a novel morphology have been fabricated using the high-shear extruder. It was found that the clay platelets were selectively dispersed in the PA11 phase with the size of larger than 200 nm, while no clay platelets were located in the PVDF phase and in the PA11 nanodomains with the size of smaller than 200 nm. Moreover, the addition of organoclay shows significant effects on the phase structure of PVDF/PA11 blends.     

Deformation and transformation mechanisms of poly(vinylidene fluoride) (PVF2)

The deformation process and the accompanyingα→β phase transformation of poly(vinylidene fluoride), drawn at 82 to 90 and 130° C, has been characterized by electron microscopy and X-ray and electron diffraction. Micronecking occurs at both draw temperatures, fibrils and mosaic blocks being drawn off the edges of the micronecks. The degree of phase transformation, at the same elongation, is dependent on the draw temperature; at 130° C the majority of the sample remains in theα phase at the natural draw ratio. The phase transformation at both draw temperatures accompanies the transformation from lamellar (block) structure to fibril.     

The creep behaviour of poly(vinylidene fluoride)/“bud-branched” nanotubes nanocomposites

The creep behaviour of poly(vinylidene fluoride) (PVDF)/multiwall carbon nanotubes nanocomposites has been studied at different stress levels and temperatures. To fine-tune the ability to transfer stress from matrix to carbon nanotubes, bud-branched nanotubes, were fabricated. The PVDF showed improved creep resistance with the addition of carbon nanotubes. However, bud-branched nanotubes showed a modified stress–temperature-dependent creep resistance compared with carbon nanotubes. At low stress levels and low temperatures, bud-branched nanotubes showed better improvement of the creep resistance than that of virgin carbon nanotubes, while at high stress levels and high temperatures, the virgin carbon nanotubes presented better creep resistance than that of bud-branched nanotubes. DSC, WAXD, and FTIR were employed to characterise the crystalline structures and dynamic mechanical properties were characterised by DMA testing. The Burgers’ model and the Findley power law were employed to model the creep behaviour, and both were found well describe the creep behaviour of PVDF and its nanocomposites. The relationship between the structures and properties was analysed based on the parameters of the modelling. The improved creep resistance for PVDF by the addition of nanotubes would benefit its application in thermoset composite welding technology.     

Nanostructure and morphology of poly(vinylidene fluoride)/polymethyl (methacrylate)/clay nanocomposites: correlation to micromechanical properties

Nanocomposites based on poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) with untreated clay were prepared in one step by reactive melt extrusion. Chemical reactions took place between the polymer matrices, the inorganic clay particles, and three reactive agents, leading to the PVDF/PMMA/clay nanocomposites. The microstructure characterizations were carried out by differential scanning calorimetry and wide-angle X-ray scattering (WAXS). The mechanical behavior was investigated by tensile experiments, impact tests, and microhardness measurements. The morphological characterization was carried out by optical and atomic force microscopy (AFM). The decrease of the melting and crystallization temperatures of the PVDF with the increasing PMMA content is attributed to the interactions between the oxygen of the PMMA carbonyl group and the PVDF’s hydrogen atom. WAXS analysis shows that there is neither an intercalation step nor total exfoliation in any composition. As the PMMA content increases, WAXS diagrams show either the PVDF α-crystallographic form, both, α- and β-forms, or only the β-form. For PMMA contents higher than 40 wt%, the materials became amorphous. The microhardness of the samples decrease for a PMMA content up to 20 wt%. The study by optical microscopy and AFM illustrates the significant effect in the presence of clay on the film’s surface morphology.     

Dielectric and magnetic properties of ferrite/poly(vinylidene fluoride) nanocomposites

Particulate composite films of poly(vinylidene fluoride) and CoFe₂O₄ and NiFe₂O₄ were prepared by solvent casting and melt processing. The well-dispersed ferrite nanoparticles nucleate the piezoelectric β-phase of the polymer, but the different ferrites nucleate the whole polymer crystalline phase at different filler concentrations. The macroscopic magnetic and dielectric response of the composites demonstrates a strong dependence on the volume fraction of ferrite nanoparticles, with both magnetization and dielectric constant increasing for increasing filler content. The β-relaxation in the composite samples is similar to the one observed for β-PVDF obtained by stretching. A superparamagnetic behavior was observed for NiFe₂O₄/PVDF composites, whereas CoFe₂O₄/PVDF samples developed a hysteresis cycle with coercivity of 0.3 T.     

Large dielectric constant and high thermal conductivity in poly(vinylidene fluoride)/barium titanate/silicon carbide three-phase nanocomposites

Dielectric polymer composites with high dielectric constants and high thermal conductivity have many potential applications in modern electronic and electrical industry. In this study, three-phase composites comprising poly(vinylidene fluoride) (PVDF), barium titanate (BT) nanoparticles, and β-silicon carbide (β-SiC) whiskers were prepared. The superiority of this method is that, when compared with the two-phase PVDF/BT composites, three-phase composites not only show significantly increased dielectric constants but also have higher thermal conductivity. Our results show that the addition of 17.5 vol % β-SiC whiskers increases the dielectric constants of PVDF/BT nanocomposites from 39 to 325 at 1000 Hz, while the addition of 20.0 vol % β-SiC whiskers increases the thermal conductivity of PVDF/BT nanocomposites from 1.05 to 1.68 W m(-1) K(-1) at 25 °C. PVDF/β-SiC composites were also prepared for comparative research. It was found that PVDF/BT/β-SiC composites show much higher dielectric constants in comparison with the PVDF/β-SiC composites within 17.5 vol % β-SiC. The PVDF/β-SiC composites show dielectric constants comparable to those of the three-phase composites only when the β-SiC volume fraction is 20.0%, whereas the dielectric loss of the PVDF/β-SiC composites was much higher than that of the three-phase composites. The frequency dependence of the dielectric property for the composites was investigated by using broad-band (10(-2)-10(6) Hz) dielectric spectroscopy.     

Morphological, viscoelastic and thermal properties of poly(vinylidene Fluoride)/POSS nanocomposites

Nanocomposites of poly(vinylidene fluoride) and polyhedral oligomeric silsesquioxane were prepared through melt blending. Morphology, viscoelastic and thermal properties were investigated. Up to 1 wt.% the processing conditions were efficient to prevent formation of large POSS agglomerates. In the nanocomposites with higher POSS contents these conditions could not avoid it, because of the strong interaction among POSS molecules. The presence of two different crystalline phases in nanocomposite was evidenced by X-ray diffraction and Fourier Transformed Infra-Red Spectroscopy. The nanocomposite with 5 wt.% content had the highest values for degree of cristallinity. The polyhedral oligomeric silsesquioxane molecules are acting as lubricant in the system, once lower values for storage modulus as well as for viscosity were observed.     

聚偏氟乙烯/有机累托土纳米复合超滤膜的制备及应用

利用溶液插层法制备了聚偏氟乙烯/有机累托土纳米复合超滤膜,研究了纳米掺杂含量对纳米片层分散状态的影响,测定了膜的各项性能,并将膜用于3种水样的处理。结果表明:纳米粘土的加入对复合膜的性能有很大影响;少量粘土的加入,能同时提高膜水通量和截留性能,在纯水通量性能测试时,其阻力增大系数由4.79下降到2.16;在对3种水样进行处理时,粘土的加入不仅能大大地提高膜在实际水处理中的抗污染能力,显著提高膜的反冲洗通量恢复率,还能获得比初始膜更好的出水水质。     

Segregated poly(vinylidene fluoride)/MWCNTs composites for high-performance electromagnetic interference shielding

Conductive polymer composites (CPCs) that contain a segregated structure have attracted significant attentions because of their promising for fulfilling low filler contents with high electromagnetic interference (EMI) properties. In the present study, segregated poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotubes (MWCNTs) composites were successfully prepared by mechanical mixing and hot compaction. The PVDF/MWCNTs samples with 7 wt% filler content possess high electrical conductivities and high EMI shielding effectiveness (SE), reaching 0.06 S cm⁻¹ and 30.89 dB (in the X-band frequency region), much higher than lots of reported results for CNT-based composites. And the EMI SE greatly increased across the frequency range as the sample thickness was improved from 0.6 to 3.0 mm. The EMI shielding mechanisms were also investigated and the results demonstrated absorption dominating shielding mechanism in this segregated material. This effective preparation method is simple, low-cost, and environmentally-friendly and has potential industrial applications in the future.     

Interface characterization and thermal degradation of ferrite/poly(vinylidene fluoride) multiferroic nanocomposites

Flexible multiferroic 0–3 composite films, with CoFe₂O₄, Ni_0.5Zn_0.5Fe₂O₄ or NiFe₂O₄ ferrite nanoparticles as filler and polyvinylidene fluoride (PVDF) as the polymer matrix, have been prepared by solvent casting and melt crystallization. The inclusion of ferrite nanoparticles in the polymer allows to obtain magnetoelectric nanocomposites through the nucleation of the piezoelectric β-phase of the polymer by the ferrite fillers. Since the interface between PVDF and the nanoparticles has an important role in the nucleation of the polymer phase, thermogravimetric analysis was used in order to identify and quantify the interface region and to correlate it with the β-phase content. It is found that an intimate relation exists between the size of the interface region and the piezoelectric β-phase formation that depends on the content and type of ferrite nanoparticles. The interface value and the β-phase content increase with increasing ferrite loading and they are higher for CoFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄ ferrite nanoparticles. The composites shows lower thermal stability than the pure polymer due to the existence of mass loss processes at lower temperature than the main degradation of the polymer. The main degradation of the polymer matrix, nevertheless, shows increased degradation temperature with increasing ferrite content.     

热致相分离制备聚偏氟乙烯膜

以聚偏氟乙烯(PVDF)为基材,选用3种稀释剂邻苯二甲酸二甲酯(DMP),间苯二甲酸二甲酯(DMIP),水杨酸甲酯(MS)为稀释剂,通过热致液-固相分离制备了微孔膜.结晶度随PVDF含量的增加先增加后降低,在40%(wt,下同)时结晶度最大.结晶温度随着PVDF-MS,PVDF-DMIP,PVDF-DMP的顺序降低.考察了不同降温条件对聚偏氟乙烯膜的结构的影响.在液-固相分离的前提下,通过不同的降温条件,得到球粒堆积的微观结构.     

Thermo-mechanical properties of poly(vinylidene fluoride) modified graphite/poly(methyl methacrylate) nano composites

Poly(methyl methacrylate) (PMMA) nano composites were synthesized by melt compounding technique. Different graphite loadings were investigated, including some treated with poly(vinylidene fluoride) (PVDF). A homogeneous dispersion of graphite throughout the PMMA matrix was observed under microscopic analysis. Thermo-gravimetric analysis showed the incorporation of graphite resulted in improvement of thermal stability of neat PMMA. Dynamic mechanical thermal analysis also showed a significant improvement in the storage modulus over the temperature range of 25–150 °C. Coating the graphite with a small amount of PVDF was found to further extend the improvement in the modulus of the PMMA nano composite at 1 wt.% graphite loading.     

A simple and controllable nanostructure comprising non-conductive poly(vinylidene fluoride) and graphene nanosheets for supercapacitor

An effective method was used to produce stable and homogeneous colloidal suspensions of highly reduced graphene oxide (RGO) in N,N-dimethylformamide (DMF) without the assistance of dispersing agents.Ac...     

Toughening and reinforcement of poly(vinylidene fluoride) nanocomposites with “bud-branched” nanotubes

Bud-branched nanotubes, fabricated by growing metal particles on the surface of multi-wall carbon nanotubes (MWCNTs), were used to prepare poly(vinylidene fluoride) (PVDF) based nanocomposites. The results of differential scanning calorimetry (DSC) showed that the introduction of the MWCNTs and bud-branched nanotubes both increased the crystallization temperature, while no significant variation of T_m (melting temperature), ΔH_c (melting enthalpy) and ΔH_m (crystallization enthalpy) occurred. The results of wide angle X-ray diffraction (WAXD) tests showed that α-phase was the dominated phase for both pure PVDF and its nanocomposites, indicating the addition of the MWCNTs and bud-branched nanotubes did not alter the crystal structures. Dynamic mechanical analysis (DMA) tests showed that bud-branched nanotubes were much more efficient in increasing storage modulus than the smooth MWCNTs. In addition, no significant variation of the T_g (glass transition temperature) was observed with the addition of MWCNTs and bud-branched nanotubes. Tensile tests showed that the introduction of MWCNTs and bud-branched nanotubes increased the modulus. However, a dramatic decrease in the fracture toughness was observed for PVDF/MWCNTs nanocomposites. For PVDF/bud-branched nanotubes nanocomposites, a significant improvement in the fracture toughness was observed compared with PVDF/MWCNTs nanocomposites.     

Preparation and proton conductivity of poly(vinylidene fluoride)/layered double hydroxide nanocomposite gel electrolytes

Layered double hydroxide (LDH) was synthesized in the presence of sodium dodecyl sulfate. X-ray diffraction (XRD) and infrared spectrum revealed that dodecyl sulfate (DS) anions were successfully intercalated into the interlayers of LDH. Poly(vinylidene fluoride)/LDH nanocomposite membranes were prepared by mixing the DS intercalated LDH with poly(vinylidene fluoride) (PVDF) in N,N’′-dimethylformamide solution followed by the solvent evaporation. The nanocomposite membranes were further swollen with a H₃PO₄ solution in ethylene carbonate-propylene carbonate to obtain the proton conducting nanocomposite gel electrolytes. XRD and transmission electron microscope results showed that LDH particles were well-dispersed in the polymer matrix and partially intercalated by polymer chains. The proton conductivity was highly enhanced in the nanocomposite gel electrolyte systems. In the case of the nanocomposite gel electrolyte containing 7.40 wt.% LDH, the proton conductivity increased by about 2.5 times compared to pure PVDF gel electrolyte.     

Multi-walled CNT-induced phase behaviour of poly(vinylidene fluoride) and its electro-mechanical properties

A simple two-step process was used to disperse acid functionalized multi-walled carbon nanotubes (CNTs) in poly(vinylidene fluoride) (PVDF). While the neat solvent-cast PVDF showed coexistence of α- and β-phases; the composite films exhibited only β-phase crystals. Further studies on the crystalline behaviour, using differential scanning calorimetry and small-angle X-ray scattering techniques showed an increase in the percentage of crystalline phase with CNT. The network formed by CNTs in the matrix reduced the macroscopic electrical resistivity of composite films. The dielectric constant increased with CNT loading. Further, these composites were investigated for its electromagnetic wave absorbance (EWA) and strain sensing properties. The EWA properties were studied in the X-band (6–12 GHz) region. A maximum of ~37 dB reflectivity loss at ~9.0 GHz was obtained in a ~25 μm thick PVDF film containing only 0.25 wt% of functionalized CNT. Preliminary studies showed a systematic change in electrical resistance by the application of dynamic bending strain in nanocomposite film. The film also showed a significant improvement in mechanical stiffness owing to efficient stress transfer from matrix to filler, the property desirable for a good strain sensor. In view of the unique combination of EWA and electro-mechanical properties, the nanocomposite films are expected to serve as a multifunctional material for strain sensing in health monitoring as well as in radar absorption.     

Morphology and phase transition of high melt temperature crystallized poly(vinylidene fluoride)

When PVDF is crystallized at temperatures above 155°C it presents a multiform morphology composed of ringed, non ringed and mixed spherulites. Infrared spectroscopy showed that the ringed spherulites are formed exclusively by the phase when crystallization takes place at temperatures below 155°C. Higher temperatures induce a solid-state phase transformation in these structures, increasing the amount of phase with crystallization time. The rate at which this transformation takes place increases with crystallization temperature. The non ringed spherulites, only formed at crystallization temperatures above 155°C, consist predominantly of the phase, crystallized from the melt, with small phase inclusions. The melt process of the different spherulites, observed by optical microscopy and calorimetric measurements (DSC) showed that the melt temperature of the phase, originated from the phase transition, is 8°C higher than that crystallized directly from the melt. Optical micrographs of samples heated up to 186°C and quickly cooled allowed visualization of the ringed spherulite regions which underwent the phase transformation at different crystallization times and temperatures.     

Etching and morphology of poly(vinylidene fluoride)

The lamellar structures within spherulites of melt-crystallized poly(vinylidene fluoride) have been examined following the development of an etching technique which allows the study of representative morphologies in this polymer. The banded -spherulites, which predominate at crystallization temperatures below 165°C, are found to be made up of densely packed lamellae with an intrinsically planar habit, whilst the -spherulites which develop preferentially at higher temperatures, have a curious architecture in which the lamellae adopt a highly curved scroll-like morphology. These observations are discussed in terms of existing models for spherulite banding and non-planar lamellar habits.