• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.319-320
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• 2003

압전성과 초전성을 나타내는 고분자인 poly(vinylidene fluoride)(PVDF)는 poly(methyl methacrylate), poly(vinyl acetate), 및 Poly(vinyl methyl ketone)(PVMK) 등과 블렌딩하면 혼화성(miscibility)이 있다. 이들 블렌드물들을 용융온도 이상으로 승온시키면 낮은 온도에서는 균일상으로 존재하지만, 온도가 계속 증가하면 상분리되어 LCST(lower critical solution temperature)를 나타낸다[1]. 이러한 승온에 의한 상분리 거동에서 외부전장을 가하면 전기활성 고분자인 PVDF에 영향을 주어 상분리 거동이 변화될 것으로 예산된다. (중략)

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.559-563
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• 2014

It is well known that $CO_2$ can be dissolved easily in imidazolium-based room temperature ionic liquids (RTILs). Because of the high $CO_2$ solubility in RTILs, membranes containing RTILs can separate easily gas mixtures such as $CO_2/N_2$ and $CO_2/CH_4$. In this study, we prepared poly(vinylidene fluoride)-hexafluoropropyl copolymer (PVDF-HFP) gel membranes with several RTILs and measured permeabilities of several gases. When the anion of ionic liquids was tetrafluoroborate($BF{_4}^-$), both $CO_2$ permeability and selectivities decreased as the carbon number of the cation increased. When the cation of ionic liquids was 1-ethyl-3-methylimidazolium[emim], $CO_2$ permeability of gel membranes containing bis(trifluoromethane) sulfoneimide($Tf_2N^-$) anion was double compared to those containing tetrafluoroborate($BF{_4}^-$) anion. However, $CO_2/N_2$ and $CO_2/CH_4$ selectivities of the $Tf_2N^-$ case were decreased, whereas the $H_2$ selectivity was almost the same for two cases.

• Korea-Australia Rheology Journal
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• v.20 no.4
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• pp.213-220
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• 2008

The effects of temperature on the rheological properties of the solutions of poly(vinylidene fluoride-co-hexafluopropylene) (PVDF-HFP) in dimethyl acetamide (DMAc) were investigated in terms of frequency and concentration. The effects of temperature on the intrinsic viscosity of the solutions were discussed. In dynamic rheological measurement, the concentrated solutions showed a little unexpected rheological response; as temperature was increased dynamic viscosity was increased and the solutions exhibited more noticeable Bingham body character over the temperature range, 30 to $70^{\circ}C$. In addition, the solution gave longer relaxation time, lower value of loss tangent and higher value of yield stress at higher temperature and at higher concentration. On the other hand, the dilute solutions revealed that intrinsic viscosity was decreased and its Huggins constant was increased with increasing temperature. These physical parameters suggested that the increase of viscosity with increasing temperature resulted from the localized gelation of PVDF-HFP due to reduced solubility to the solvent.

• Membrane and Water Treatment
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• v.1 no.3
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• pp.215-230
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• 2010

Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique using different polyethylene glycol (PEG) concentrations as non-solvent additive in the dope solution. Two different PEG concentrations (3 and 5 wt.%). The morphology and structural characteristics of the hollow fiber membranes were studied by means of optical microscopy, scanning electron microscopy, atomic force microscopy (AFM) and void volume fraction. The experimental permeate flux and the salt (NaCl) rejection factor were determined using direct contact membrane distillation (DCMD) process. An increase of the PEG content in the spinning solution resulted in a faster coagulation of the PVDF-HFP copolymer and a transition of the cross-section internal layer structure from a sponge-type structure to a finger-type structure. Pore size, nodule size and roughness parameters of both the internal and external hollow fiber surfaces were determined by AFM. It was observed that both the pore size and roughness of the internal surface of the hollow fibers enhanced with increasing the PEG concentration, whereas no change was observed at the outer surface. The void volume fraction increased with the increase of the PEG content in the spinning solution resulting in a higher DCMD flux and a smaller salt rejection factor.

• Polymer(Korea)
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• v.33 no.6
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• pp.544-550
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• 2009

In this study, we have designed [Epoxy/PEG] polymer gel electrolyte systems by thermal curing the mixtures of epoxy, PEG, imidazole catalyst, and a plasticizer of 1:1 ethylene carbonate and propylene carbonate in the presence of $LiPF_6$ salt. In order to enhance the poor mechanical property of the Corresponding [Epoxy/PEG] gel electrolyte PVdF-HFP was incorporated into the system. The ionic conductivities of the polymer gel electrolytes were related to the amount of PVdF-HFP in blends as well as the amount of liquid electrolyte. The optimized gel system showed room-temperature conductivities of $2.56\times10^{-3}S/cm$.

• Membrane Journal
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• v.28 no.3
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• pp.187-195
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• 2018

In this work, the morphology of polyvinylidene-co-hexafluoropropylene (PVDF-co-HFP) membranes were systemically investigated using phase inversion technique, to target membrane contactor applications. As the presence of macrovoids degrade the mechanical integrity of the membranes and jeopardize the long-term stability of membrane contactor processes (e.g. wetting), a wide range of dope compositions and casting conditions was studied to eliminate the undesired macrovoids. The type of solvent had significant effect on the membrane morphology, and the observed morphology were correlated to the physical properties of the solvent and solvent-polymer interactions. In addition, to fabricate macrovoid-free structure, the effects of different coagulation temperatures, inclusion of additives, and addition of nonsolvents were investigated. Due to the slow crystallization rate of P(VDF-co-HFP) polymer, it was found that obtaining porous membrane without macrovoids is difficult using only nonsolvent-induced phase separation method (NIPS). However, combined other phase inversion methods such as evaporation-induced phase separation (EIPS) and vapor-induced phase separation (VIPS), the desired membrane morphology can be obtained without any macrovoids.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.327-328
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• 2003

최근, 가정 안까지 고속광통신망이 구축되면서 폴리머광섬유 (polymer optical fiber, POF)에 대한 관심이 매우 증가하고 있다[l,2] POF는 빛을 전송하는 코어층과 내부전반사를 유도하면서 코어를 보호하는 클래드 층으로 구성되어 있다. 빛을 직접 전송하지 않으나 POF가 최적의 성능을 보이기 위해서는 적절한 클래드 선택이 중요하다. 그러나 PVDF/PMMA 블렌드, fluoroacrylate, VDF-HFP 공중합체 등이 클래드용 재료로 사용되고 있다는 사실만이 알려져 있을 뿐 보다 자세한 정보는 보고된 바 없다. (중략)

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.65-66
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• 2006

[ $TiO_2$ ] single crystalline nanorods are prepared from electrospun fibers which are composed of nanofibrils with an island-in-a-sea morphology. The mechanical pressure produces each fibril into nanorods which are converted to anatase single crystals after calcinations. HRTEM shows that the (001) plane is growing along the longitudinal direction of the rod. In this work, the nanorod electrode provides the efficient photocurrent generation in a quasi-solid state dye-sensitized solar cells (DSSCs) using highly viscous PVDF-HFP based gel electrolytes. The overall converision efficiency of the $TiO_2$ nanorods shows 6.2 % under $100\;mW/cm^2$ (AM 1.5G) illumination.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.320-320
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• 2010

The dye-sensitized solar cells (DSSCs) have achieved so far the highest validated efficiency over 11%. However, the cells with the best performance utilize volatile solvent as a electrolyte, which can cause some practical limitations for the long-term operation. This is one of the most substantial problems to be resolved for the commercialization of DSSCs. In order to improve the long-term stability, many research groups have reported new electrolyte system, to replace the liquid type electrolyte by non-volatile ones. In this work, we studied long-term stability of the DSSCs with various types of electrolytes such as (PVDF HFP) based polymer, eutectic melts of ionic liquids, and liquid based solvent. The cells with various electrolytes have been exposed to the condition under thermal stress and illumination over 1000 hours. We will report the change of photovoltaic properties with time and investigate the degradation mechanism with the impedance spectroscopic analysis.

• Composites Research
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• v.35 no.3
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• pp.216-221
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• 2022

Recently, the worldwide demand for disposable masks has increased due to COVID-19 infections and severe air pollution. Personal masks should reduce breathe resistance while maintaining filtering performance. In this study, a solution blowing process is used to produce composite nanofiber filters to co-spin two polymers at once. The manufacture process of the various fiber diameter filter was designed, and the filtration performance and differential pressure of the prepared filter was investigated. Poly vinylidene fluoride-hexafluoropropylene (PVDF-HFP) and Polylactic acid (PLA) fibers were chosen to be entangled together in a layer with a diameter of 1.05 ㎛ and 0.33 ㎛. Composite nanofilters showed up to 87% filtration efficiency and 32 Pa differential pressure.