PMMA/PVDF共混对PVDF的β相构型影响的研究

采用溶液法制备了不同含量的聚甲基丙烯酸甲酯/聚偏二氟乙烯(PMMA/PVDF)共混薄膜,利用傅立叶变换红外光谱(FTIR)、X射线衍射谱(XRD)、和差热分析法(DSC)对共混薄膜的结晶行为进行了分析。结果表明,共混物中PMMA的含量对PVDF的β相构型有明显影响:PMMA/PVDF=30/70共混物中β相含量最高。为提高PVDF薄膜的铁电性能提供了新的研究方法。     

Evaluation of piezoelectric PVDF polymers for use in space environments. II. Effects of atomic oxygen and vacuum UV exposure

The effects of atomic oxygen (AO) and vacuum UV radiation simulating low Earth orbit conditions on two commercially available piezoelectric polymer films, poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐TrFE), have been studied. Surface erosion and pattern development are significant for both polymers. Erosion yields were determined as 2.8 × 10^?24 cm³/atom for PVDF and 2.5 × 10^?24 cm³/atom for P(VDF‐TrFE). The piezoelectric properties of the residual material of both polymers were largely unchanged after exposure, although a slight shift in the Curie transition of the P(VDF‐TrFE) was observed. A lightly cross‐linked network was formed in the copolymer presumably because of penetrating vacuum ultraviolet (VUV) radiation, while the homopolymer remained uncross‐linked. These differences were attributed to varying degrees of crystallinity and potentially greater absorption, and hence damage, of VUV radiation in P(VDF‐TrFE) compared with PVDF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2503–2513, 2005     

Poly(vinylidene fluoride)/polycarbonate blend-based nanocomposites with enhanced rigidity — Selective localization of carbon nanofillers and organoclay

Carbon nanotube (CNT), graphene nanoplatelet (GnP) and organo-montmorillonite (15 A) individually and simultaneously served as reinforcing fillers to prepare poly (vinylidene fluoride) (PVDF)/polycarbonate (PC) blend-based multicomponent nanocomposites. Scanning electron microscopy and transmission electron microscopy results confirmed the selective localization of individual and hybrid fillers within the PC domains. Some 15 A was located at the interface of PVDF/PC phases to modify the blend morphology. Addition of CNT led to the development of a quasi co-continuous PVDF-PC morphology. Differential scanning calorimetry results showed that 15 A, not CNT/GnP, facilitated PVDF crystallization in the composites. Among the fillers, 15 A alone induced β-form PVDF crystals, as revealed by the X-ray diffraction results, and consequently caused the complex crystallization and melting of PVDF. The rigidity (Young's and flexural moduli) of the PVDF/PC blend increased after the formation of various blend-based nanocomposites. The hybrid filler of CNT/15 A increased the Young's modulus by approximately 90% compared with that of the blend. Rheological property measurements confirmed the formation of a pseudo-network structure in the composites. Adding CNT increased the complex viscosity of the samples to a higher extent than did adding GnP, and the viscosity further increased with the co-existence of carbon nanofiller(s) and 15 A.     

离子液体/聚偏氟乙烯纳米纤维的防结冰性能

通过静电纺丝方法制备了掺杂离子液体([BMIM][PF₆])的聚偏氟乙烯(PVDF)纳米纤维. 研究结果表明, [BMIM][PF₆]与PVDF具有相互作用, 并可促进PVDF形成β相晶体. 在溶剂挥发后, 离子液体存在于PVDF纳米纤维的表面. 纳米纤维中的离子液体含量对复合纳米纤维的表面形态和润湿性具有显著影响. 通过离子液体的引入, 可有效推迟水滴在纳米纤维表面的结冰时间, 降低水滴的结晶温度, 并且降低冰黏附强度. 研究结果显示含有10%[BMIM][PF₆]的PVDF纳米纤维疏水性最高, 并具有优异的防结冰性质.     

Poly（vinylidene fluoride）/Clay Nanocomposites by Melt Compounding

The crystalline structures, morphologies, and mechanical properties of poly（vinylidene fluoride）/clay nanocomposites were studied using X-ray diffraction（XRD）, transmission electron microscopy（TEM）, Fourier transform infrared spectroscopy（FTIR）, polarized optical microscopy（POM）, and tensile tests. The results of XRD and TEM show that organoclays are dispersed in the poly（vinylidene fluoride）（PVDF） matrix. A clay-induced crystal transformation from α-phase to β-phase of PVFD was confirmed by XRD and FTIR. Clay layers restricted the growth of spherulite. The tensile tests indicate that the tensile modulus and yield strength as well as the elongation at break decrease when clay is loaded.     

Effect of thermal treatment on the characteristics of electrospun PVDF−silica composite nanofibrous membrane

Composite nanofibrous membranes were prepared by the electrospinning and the thermal treatment from poly(vinylidene fluoride) (PVDF)-tetramethyl orthosilicate (TMOS) blend solutions. The average diameter of nanofibers was reduced with increasing the concentration of TMOS in the solution due to the decrease of the solution viscosity. The EDX spectra confirmed the presence of TMOS on the external surface of the composite nanofibrous membrane. The porosity of membranes was effectively enhanced by the introduction of electrospinning technique. However, the mechanical properties, thermal stability and hydrophobicity were not markedly amplified. Thus the thermal treatment of the composite membranes was carried out, leading to the enormous enhancement of the mechanical properties and hydrophobicity. In addition, XRD results revealed that the crystal structure of PVDF in the composite membranes transformed from α-phase to β-phase due to the formation of silica particles by the thermal treatment.     

Effects of partial replacement of silicone rubber with flurorubber on properties of dynamically cured poly(vinylidene fluoride)/silicone rubber/flurorubber ternary blends

Blends of poly(vinylidene fluoride) (PVDF), silicone rubber (SR) and flurorubber (FKM) were prepared via peroxide dynamic vulcanization. The effect of FKM loading on the morphology, mechanical properties, crystallization behavior, rheology and dynamic mechanical properties of the PVDF/SR/FKM ternary blends was investigated. A “network” was observed in the PVDF/SR binary blends, which disappeared in the ternary blends, but a core-shell-like structure was formed. The mechanical properties were significantly improved. The Izod impact strength of PVDF/SR/FKM blend with 19 wt% FKM was 18.3 kJ/m², which was 3–4 times higher than the PVDF/SR binary blend. The complex viscosity and storage modulus of the PVDF/SR/FKM blends decreased with increasing FKM content, hence the processability was improved. The increase of FKM content seemed to show a favorable effect on the crystallization of the PVDF component. It promoted the nucleation process of PVDF, leading to increased polymer crystallization rate and higher crystallization temperature. The glass-rubber transition temperature of the PVDF phase moved to a lower temperature.     

Phase transformation to β-poly(vinylidene fluoride) by milling

Cryogenic mechanical milling successfully converted α-phase poly(vinylidene fluoride) (PVDF) powder into β-phase PVDF, as measured by wide-angle X-ray diffraction. The presence of β-phase PVDF became more pronounced with increased milling times over the limited time range evaluated. This was the first recorded instance of β-phase powders forming from the α phase through milling. These β-phase powders maintained their crystal structure during compression molding at 70 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 91–97, 2004     

Thermal stability of poly(vinylidene fluoride) films pre-annealed at various temperatures

This paper investigates the relationship between the pre-annealing conditions and the thermal stability of uniaxially-drawn poly(vinylidene fluoride) (PVDF) films in order to clarify their technical limits in terms of temperatures that can be used for assembly processes and for practical applications. Specimens that are pre-annealed below their melting temperature apparently shrink in the stretch-direction when they are exposed to elevated temperatures above the pre-annealing temperature. Since the content of β-PVDF in the films decreases simultaneously with the shrinkage, their piezoelectric properties also deteriorate. In addition, there is a suggestion that the level of polarization in the remaining β-phase decreases significantly during annealing above 90-100 °C. However, the dimensions and the piezoelectric coefficients of the films remain stable during annealing below the pre-annealing temperature. Therefore, the thermal stability of PVDF films can be controlled practically by using the appropriate pre-annealing temperature. By contrast, the films were softened at 90-100 °C when the pre-annealing treatment was conducted above the melting temperature. The softening of films that are pre-annealed above the melting temperature is a different phenomenon from that observed in specimens that are pre-annealed below the melting temperature.     

Crystallization behavior and hydrophilicity of poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA)/poly(styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) (SAN) ternary blends

Compatibilization of the partially miscible poly(vinylidene fluoride) (PVDF)/poly(styrene-co-acrylonitrile) (SAN) pair by a third homopolymer, i.e., poly(methyl methacrylate) (PMMA), was investigated in relation to cross section morphology, crystallization behaviors and hydrophilicity of the polyblends. Scanning electron microscopy showed a more regular and homogeneous morphology when more than 15 wt.% PMMA was incorporated. The samples presented only α phase regardless of PMMA content in the blend. As the PMMA content increased in the blends, the interactions between each component were enhanced, and the crystallization of PVDF was limited, leading to a decreasing of the crystallinity and the crystallite thickness. Besides, the hydrophilicity of PVDF was further improved by PMMA addition. The sample containing 15 wt.% PMMA showed a more hydrophilic property due to the more polar part of surface tension induced by PMMA addition. Observed from the cross section of the blends, the miscibility of partially miscible PVDF/SAN blends were efficiently improved by PMMA incorporation.     

Effect of MMT,SiO2, CaCO3, and PTFE nanoparticles on the morphology and crystallization of poly(vinylidene fluoride)

The crystallization and melting behaviors of poly (vinylidene fluoride) (PVDF) with small amount of nanoparticles (1 wt %), such as montmorillonite (MMT), SiO₂, CaCO₃, or polytetrafluoroethylene (PTFE), directly prepared by melt‐mixing method were investigated by scanning electron microscopy (SEM), polarizing optical microscopy, Fourier transform infrared spectroscopy, wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The nanoparticle structure and the interactions between PVDF molecule and nanoparticle surface predominated the crystallization behavior and morphology of the PVDF. Small amount addition of these four types of nanoparticles would not affect the original crystalline phase obtained in the neat PVDF sample (α phase), but accelerated the crystallization rate because of the nucleation effect. In these four blend systems, MMT or PTFE nanoparticles could be well applied for PVDF nanocomposite preparation because of stronger interactions between particle surface and PVDF molecules. The nucleation enhancement and the growth rate of the spherulites were decreased in the order SiO₂ > CaCO₃ > PTFE > MMT. The melting and recrystallization of PVDF was found in MMT addition sample, because of the special ways of ordering of the PVDF chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Polymerisation of vinylidene fluoride in supercritical carbon dioxide: Formation of PVDF macroporous beads

Poly(vinylidene fluoride) (PVDF) macroporous beads with diameter in the range of hundreds of micrometers were produced by batch polymerisation of vinylidene fluoride (VDF) in supercritical carbon dioxide (scCO₂) using diethyl peroxydicarbonate (DEPDC) as a free radical initiator. The rate and type of stirring were found to influence strongly the morphology of polymers, and the results indicated that the shear force was the key factor. A low shear force and a suitable monomer concentration range at 6-8 mol/l were needed for the formation of PVDF macroporous beads. Scanning electron microscopy (SEM) was employed to characterize the polymer morphology, and Brunauer-Emmett-Teller (BET) method was used to analyze the surface area of the polymer macroporous beads. In addition, polydimethylsiloxane monomethylacrylate (PDMS-ma) and poly(1H,1H,2H,2H-perfluorooctyl methacrylate) (PFOMA) were found to be able to control the size of PVDF macroporous beads. We propose that the formation of PVDF macroporous beads results from the aggregation of semi-crystalline PVDF primary particles.     

具有纳米结构的聚偏氟乙烯/1-乙烯基-3-丁基咪唑氯盐离子液体复合材料的结晶行为

用示差扫描量热(DSC)、偏光显微镜(POM)及X射线衍射(XRD)分析考察了具有纳米结构的聚偏氟乙烯(PVDF)/1-乙烯基-3-丁基咪唑氯盐离子液体([VBIM][Cl])复合材料(PVDF/[VBIM][Cl])中经[VBIM][Cl]接枝的PVDF(PVDF-g-[VBIM][Cl])纳米微区对PVDF结晶行为的影响.研究结果表明,[VBIM][Cl]化学接枝在PVDF的分子链上,在PVDF/[VBIM][Cl]复合材料中,PVDF-g-[VBIM][Cl]嵌段形成大量纳米微区,分散在PVDF基体中.PVDF-g-[VBIM][Cl]纳米微区能够显著提高PVDF熔体结晶温度(Tc)并显著降低PVDF晶体的等温结晶时间.与纯PVDF相比,在纳米结构的PVDF/[VBIM][Cl]复合材料中,PVDF-g-[VBIM][Cl]纳米微区大大提高了PVDF晶体的成核速率,PVDF的球晶尺寸明显减小.由于[VBIM][Cl]完全"受限"于PVDF-g-[VBIM][Cl]纳米微区中,无法与PVDF分子链发生相互作用,因此纳米结构的PVDF/[VBIM][Cl]复合材料最终以非极性的α晶体为主.由于PVDF-g-[VBIM][Cl]纳米微区与PVDF基体具有热力学不相容性,因此其界面处的PVDF分子链处于部分有序的状态,有助于PVDF晶体的成核,加速了PVDF晶体的结晶速率.     

Effect of low contents of a polyaniline derivative on the crystallization and electrical properties of blends with PVDF

The effect of low levels of poly(o‐methoxyaniline) (POMA) on the crystallization, morphology, and electrical characteristics of blends with poly(vinylidene fluoride) (PVDF) were studied by infrared spectroscopy, AC electrical measurements, and optical microscopy. Undoped POMA has a strong effect in increasing the α‐phase and decreasing the β‐phase content of PVDF in blends crystallized from solution. For blends melt crystallized, doped POMA promotes much greater homogeneity than undoped POMA. Interestingly, doped POMA promotes the nucleation and growth of unringed PVDF spherulites, whereas undoped POMA hinders it. The doping state of the POMA was also extremely important in determining the electrical behavior of the blend. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1219–1224, 1999     

Miscibility and ferroelectric behavior in blends of poly(vinylidene fluoride/trifluoroethylene) and poly(vinyl acetate)

The blend system containing a poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)] copolymer (68/32 mol %) and poly(vinyl acetate) (PVAc) was miscible from the results of differential scanning calorimetry (DSC) studies that exhibit the presence of a single, composition‐dependent glass transition temperature (T_g) and a strong melting point depression for the semicrystalline P(VDF/TrFE) component. However, differences between the DSC and dielectric measurements, which showed a separate P(VDF/TrFE) T_g peak, suggests that the P(VDF/TrFE)/PVAc blends are actually partially miscible. Because of the lower dielectric constant of PVAc and the reduced sample crystallinity caused by the addition of PVAc, both the dielectric constant and the remanent polarization of the copolymer blends decrease with increasing PVAc content. The presence of a small amount of PVAc stabilized the anomalous ferroelectric behavior of ice–water‐quenched P(VDF/TrFE), and the blend portrayed normal polarization reversal behavior after adding only 1 wt % PVAc. The piezoelectric response suggests small changes with an increasing number of poling cycles. It is believed that PVAc affects the D‐E hysteresis behavior at the interface between crystalline and amorphous phases, although much work remains to be done to confirm this hypothesis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 927–935, 2003     

Microfluidic fabrication of β-phase enriched poly(vinylidene fluoride) microfibers toward flexible piezoelectric sensor

β-phase enriched piezoelectric poly(vinylidene fluoride) (PVDF) films/fibers are often prepared by high-energy costing methods, including mechanical stretching, high-electric field or electrospinning. In this study, PVDF piezoelectric microfibers, for the first time, were prepared by microfluidic spinning technology. The β-phase enriched PVDF microfibers with various diameters could be easily obtained inside the microfluidic channel due to the mass transfer induced phase inversion of the inner PVDF solution. The influence of diameter of the fibers, PVDF concentration of the inner phase and water content of the outer phase on the β-phase content and crystallinity degree of the obtained fibers was studied in detail. The obtained β-phase enriched fiber was weaved into meshes. Flexible piezoelectric fabrics were then developed based on these meshes, and further used as in-situ and real time human motion monitoring. This simple and effective strategy provides a promising microfluidic spinning technique toward the development of functional microfibers and wearable piezoelectric sensors, which may also give some implies for the industrial wet-spinning of piezoelectric PVDF fibers in the future.     

Preparation and properties of dynamically cured poly(vinylidene fluoride)/silicone rubber blends

Blends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through dynamic vulcanization. The effects of SR content on crystallization behavior, rheology, dynamic mechanical properties and morphology of the blends were investigated. Morphology characterization shows that the crosslinked spherical SR particles with an average diameter of 2-4 μm form a “network” in the PVDF continuous phase. The dynamic mechanical properties indicate the interface adhesion between PVDF and rubber phase is improved by the dynamic vulcanization. The rheology study shows that with the increase of rubber content the blends pseudoplastic nature is retained, while the viscosity increases, and hence the processability is less good. The incorporation of SR phase promotes the nucleation process of PVDF, leading to increased polymer crystallization rate and crystallization temperature. However, a higher content of SR seems to show a negative effect on the crystallinity of the PVDF component.     

Structure and pH‐sensitive properties of poly (vinylidene fluoride) membrane changed by blending poly (acrylic acid) microgels

pH‐sensitive poly (vinylidene fluoride) (PVDF)/poly (acrylic acid) (PAA) microgels membranes are prepared by phase inversion of the N, N‐dimethylformamide solution containing PAA microgels and PVDF in aqueous solution. The composition and structure of the blend membrane are investigated by Fourier transform infrared spectra, X‐ray photoelectron spectroscopy measurements, thermo gravimetric analysis, field‐emission scanning electron microscope and atomic force microscope. The results indicate the surface and cross section of the blend membranes have a porous structure with PAA microgels immobilized inside the pore and on the membrane surface. The blend PVDF membranes exhibit pH‐sensitive water flux, with the most drastic change in permeability observed between pH 3.7 and 6.3. The blend membranes are fouled by bovine serum albumin, and their antifouling property is enhanced by increasing PAA microgels, mainly derived from the improved hydrophilic property. Copyright © 2013 John Wiley & Sons, Ltd.     

Evident improvements in the rigidity,toughness, and electrical conductivity of PVDF/HDPE blend with selectively localized carbon nanotube

In this work, carbon nanotube (CNT) was used to fabricate poly(vinylidene fluoride) (PVDF)/high density polyethylene (HDPE) blend-based nanocomposites via a Haake mixer. Scanning electron microscopy confirmed that the CNT was mainly selectively located in the HDPE dispersed domains. Thermogravimetric analysis revealed that CNT addition improved the thermal stability of the blend (up to 61 °C increase at 3-phr CNT loading at 40 wt% loss) in air environment. Differential scanning calorimetry results revealed the enhanced nucleation of individual PVDF and HDPE upon crystallization in the composites; the presence of CNT inceased the stability of PVDF crystals. CNT addition increased the heat distortion temperature of the blend by up to 27 °C at 3-phr CNT loading. The complex viscosity and storage modulus increased due to the CNT pseudo-network formation in the reduce-sized HDPE phase of the composites. The rigidity of the blend was significantly improved after the addition of CNT. The impact strength of the blend increased by up to 66% after 2-phr CNT loading, and the electrical resistivity of the blend decreased by up to nine orders at 3-phr CNT loading due to the double percolation-like morphology formation.     

Influence of size reduction of crosslinked rubber particles on phase interface in dynamically vulcanized poly (vinylidene fluoride)/silicone rubber blends

In this paper, the influence of rubber particle size on the phase interface in dynamically vulcanized poly(vinylidene fluoride)/silicone rubber (PVDF/SR) blends without any modifier is discussed through the studies of specific surface of crosslinked SR particles, crystallization behavior and crystal morphology of the PVDF phase, interfacial crystallization, melt rheological behavior and mechanical properties of blends. A series of decreased average particle size was successfully obtained by control of rotor rate. It was found that properly high rotor rate helped to achieve a reduced particle size and a narrowing size distribution. The reduced SR particle size enlarged the PVDF/SR interface which has a positive effect on the interfacial crystallization and the melt rheological behavior. At high SR content, the negative effect of the poor interface interactions played the dominate role on determining the mechanical properties. However, the blend exhibited a unique stiffness-toughness balance at the PVDF/SR = 90/10. We hope that the present study could help to lay a scientific foundation for further design of a useful PVDF/SR blend with promoted properties to partly replace the high-cost synthetic fluorosilicone materials.