Crystalline Structure Of PVDF Research Articles

분산코팅에 의해 형성된 Poly(vinylidene fluoride)와 Poly(methyl methacrylate) 블렌드 코팅층의 표면 특성

본 연구에서는 poly(ethylene terephthalate)(PET) 필름을 기재로 하여 분산코팅에 의해 형성된 poly(vinylidene fluoride)(PVDF)와 poly(methyl methacrylate)(PMMA) 블렌드 코팅의 표면 특성을 관찰하였다. 분산코팅의 특성상 저온에서 형성된 블렌드 코팅은 PVDF 입자의 형태와 결정구조가 그대로 유지되었으나 <TEX>$120^{\circ}C$</TEX> 이상의 코팅온도에서 형성된 코팅의 경우 블렌드에 포함되어 있는 PVDF의 양에 따라 다양한 표면 특성을 나타내었다. 블렌드 중 PVDF의 양이 80 wt% 이상인 경우 PVDF의 <TEX>${\alpha}$</TEX>-결정구조에 의한 특성이 확실히 관찰되는 반면에 PMMA의 양이 증가하면 표면 형태와 결정구조의 변화가 변화하는 것을 관찰하였다. 또한 코팅층의 최외각 표면에 대한 XPS 분석결과는 분산코팅에서도 PVDF의 표면 이행성이 나타남을 보여준다. Surface properties such as morphology, crystalline structure, and chemical composition of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend coatings prepared by dispersion coating on poly(ethylene terephthalate) (PET) film have been investigated. It was observed that the surface properties were greatly influenced by the coating temperature and blend composition according to SEM, ATR-FTIR and XPS analysis. The typical surface morphology of <TEX>${\alpha}$</TEX>-crystalline structure of PVDF could be observed when the coating temperature was lower than <TEX>$120^{\circ}C$</TEX> or the amount of PVDF was higher than 80 wt% in the blend. Otherwise, the crystalline structure was changed from <TEX>${\alpha}$</TEX>-crystal to <TEX>${\gamma}$</TEX>-crystal or amorphous state. Based on the XPS analysis, the surface segregation of PVDF chains in the blend coating was confirmed.

PS19 Drop &amp; Dry法によるβ型Poly(vinylidene fluoride)フィルムの作成

We confirmed the presence of beta-phase of Poly(vinylidene fluoride) (PVDF) crystals when a PVDF solution was dropped on a substrate, then dried and formed as film (drop & dry fabrication). This study was conducted to investigate the beta-phase PVDF formation mechanism in drop & dry fabrication technique. First, PVDF films were fabricated by drop & dry fabrication technique. Second, their PVDF crystalline structure was analyzed using x-ray diffraction device. The presence of beta-phase PVDF crystals depends on the initial solution state and dry condition. Therefore, the effect of PVDF concentration in the solution, the quantity of the solution drop, and drying speed on beta-phase PVDF crystal formation was investigated, and the formation mechanism was discussed with the present experimental results.

Electrically excited oscillation and crystalline structure of a nanoclay/poly(vinylidene fluoride) composite film

This study was conducted to investigate electrically excited oscillation and crystalline structure of nanoclay/poly(vinylidene fluoride) (PVDF) composite films. First, nanoclay/PVDF composite films are fabricated by solvent casting. Second, their PVDF crystalline structure and nanoclay orientation are analyzed using x-ray diffraction. The impedance characteristics of films are then measured. Third, the oscillation excited from films as a result of applied voltage is measured. Thereby, we confirmed the presence of unoriented β-phase PVDF crystals and exfoliated-type nanoclay structure in a composite film. The output oscillation showed monotonic component corresponding to the input sinusoidal voltage at a high frequency range, although its amplitude is low.

Effect of multiwalled carbon nanotubes on crystallization behavior of poly(vinylidene fluoride) in different solvents

AbstractIn this study, the poly(vinylidene fluoride) (PVDF)—multiwalled carbon nanotubes (MWNTs) composites have been prepared by solution casting in two different solvents: dimethyl sulfoxide (DMSO) and dimethylacetamide (DMAc). Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) results showed that the crystal phases of PVDF are quite different in the two solvents. When DMSO is used as the solvent, the PVDF crystalline phases could be greatly alternated from α‐form to β‐form by the incorporation of MWNTs. While the crystalline structure of PVDF hardly change in the case of DMAc. The DSC and polarized optical microphotographs implied that MWNTs not only act as nucleating agents for PVDF but also confine the crystallization of PVDF. Besides, it was found that the storage modulus (E′) of the composites were significantly enhanced with an appropriate content of MWNTs. And when using DMSO as the solvent, one relaxation process emerges in the loss tan δ (loss factor) curves of the neat PVDF and PVDF/MWNTs composites, while it was not observed in the DMAc system. The obtained results revealed that varing solvents have different effects on the crystallization behavior of PVDF with the addition of MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of multi‐walled carbon nanotubes on crystallization, thermal, and mechanical properties of poly(vinylidene fluoride)

AbstractComposites were prepared by solution blending poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWNTs). Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) results showed that the crystalline structure of PVDF was changed by the addition of MWNTs and a MWNTs‐induced crystal transformation from α‐phase to β‐phase of PVDF was confirmed. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMA) techniques, thermal and mechanical properties of the composite films were examined. As the DSC results showed, addition of MWNTs would lead to the increased cooling crystallization temperature (Tc), implying that MWNTs nanoparticles could act as nucleating agents, which is further proved with the help of polarized optical microphotographs. On the other hand, the decreasing of Dd (degree of crystallinity) implied that the MWNTs networks can confine the crystallization of PVDF. Through the curve analysis of the dynamic mechanical measurements, it was found that the storage modulus (E′) is significantly enhanced, revealing that a strong interaction should exist between PVDF and MWNTs. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Preparation of PVDF/PMMA blend hollow fiber membrane via thermally induced phase separation (TIPS) method

Porous poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend hollow fiber membranes were prepared via thermally induced phase separation (TIPS) process. From the measurement of X-ray diffraction, the crystalline structure of PVDF hardly changed by blending with PMMA. When total polymer concentration was fixed at 30 wt%, water permeability of the blend membrane increased by increasing PMMA concentration. However, when PVDF concentration was fixed at 25 wt%, the trend of water permeability with the increase of PMMA concentration was contrary to the former case. Treating with acetone was applied to extract the PMMA from the obtained blend membranes. The extraction of PMMA was effective to increase water permeability. In addition, the extraction of PMMA brought about the improvement for the membrane elongation. The PVDF crystallinity was found to increase with the PMMA extraction due to the secondary crystallization. This was the reason for the elongation enhancement.

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.

Structural characteristics of poly(vinylidene fluoride)/clay nanocomposites

Poly(vinylidene fluoride) (PVDF)/clay nanocomposites with different clay contents were prepared by melt intercalation. The effects of clay on crystalline structure of PVDF were characterized, compared and discussed. For the nanocomposite containing 0.4 wt.% clay, the α phase coexists with the γ phase in the PVDF matrix in room temperature, however, the γ phase is unstable at 160 °C. When clay contents in the nanocomposites are greater 1 wt.%, the α phase coexists with the β phase. The β phase remains unchanged even after annealing. With increasing clay content, the location of the (021) reflection of α phase shifts to lower angle, while that of the (002) refection shifts to higher angle. Clay loading also induces the imperfection of α crystals. The results are attributed to the nucleation of PVDF on nanometer-size clay layers and the confining effect of nanometer-size clay on PVDF.

Effect of surface modification of nanosilica on crystallization, thermal and mechanical properties of poly(vinylidene fluoride)

Composites were prepared by solution blending ploy(vinylidene fluoride) (PVDF) and nanosilica which modified by different organic modifiers. Infrared analysis showed that the crystalline structure of PVDF was changed by the addition of RNS-A (silica with amino terminated group), while similar crystalline structure as pure PVDF was observed for composites with DNS-0 and DNS-2, unmodified silica and alkyl terminated group silica, respectively. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMTA) techniques, crystalline structure, thermal, and mechanical properties of the composite films were examined. As the DSC results showed, addition of SiO2 would lead to the increased cooling crystallization temperature (Tc), implying that SiO2 nanoparticles could act as nucleating agents, however the degree of crystallinity of PVDF was not elevated significantly. In the complementary modulated DSC curves, multi-melting peaks associated with non-reversing portion were observed and were explained from the viewpoint of melting-recrystallization in the DSC heating scan. In addition, dynamic mechanical properties as well as the thermal stability of the composites are also influenced by SiO2. As manifested by the corresponding DMTA and thermogravimetric analysis (TGA) results, a strong interaction should exist between PVDF and SiO2 nanoparticles.

Morphology, crystalline structure, and properties of poly(vinylidene fluoride)/silica hybrid composites

AbstractPoly(vinylidene fluoride)/silica (PVDF/SiO2) hybrid composite films were prepared via sol–gel reactions from mixtures of PVDF and tetraethoxysilane in dimethylacetamide. Their morphology, crystalline structure, and thermal, mechanical, and electrical properties were examined. For morphology measurements, scanning electron microscopy and optical microscopy were applied. X‐ray diffraction and infrared analyses showed that the crystalline structure of PVDF was not changed much by the addition of SiO2, indicating that there was no interaction between PVDF and SiO2. With increasing SiO2 content, the melting temperature rarely changed, the degree of crystallinity and the dielectric constant decreased, and the decomposition temperature slightly increased. A PVDF/SiO2 hybrid composite film with 5 wt % SiO2 exhibited balanced mechanical properties without a severe change in the crystalline structure of PVDF, whereas for the hybrid composites with higher SiO2 contents (&gt;10 wt %), the mechanical properties were reduced, and the spherulite texture of PVDF was significantly disrupted by the presence of SiO2 particles. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 40: 19–30, 2002

Factors determining the formation of the β crystalline phase of poly(vinylidene fluoride) in poly(vinylidene fluoride)-poly(methyl methacrylate) blends

Factor analysis of infrared spectra of poly(vinylidene fluoride)-poly(methyl methacrylate) blends indicates the presence of specific interactions in the melt state. The presence of a band at 882 cm−1 in the interaction spectrum of the melted blend indicates that trans sequences of poly(vinylidene fluoride) (PVDF) in the melt state can increase upon addition of poly(methyl methacrylate) (PMMA), which is highly responsible for the preferential formation of the β phase upon quenching the melted blends. The drastic reduction of the rate of crystallization upon addition of PMMA is another cause which favours the formation of the β crystalline phase. The critical quenching temperature above which the formation of the β phase was rapidly reduced is 0° C for neat PVDF, whereas it was found to be 30 or 55° C for the PVDF-PMMA blends. The percentage of PMMA which gives the maximum β-phase content was found to be around 20 wt.%. It was not PMMA, but the solvent dimethylformamide which affected the crystalline form of PVDF in the case of the samples solvent-cast and annealed. A new method to determine the contents of α- and β-phases in the PVDF-PMMA blends was proposed and used to estimate more quantitatively the effects of quenching temperature and composition on the crystalline structure of PVDF in the blends.