The changes in the crystalline structure of polyvinylidene fluoride (PVDF) were investigated via preparation of its blends with polymethyl methacrylate (PMMA), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) in molten states in an internal mixer at 10% to 40 wt% of the last two polymers. In all the blends, an increase in β-crystal content of PVDF was observed at different degrees and different morphologies. Polyvinylidene fluoride blends with PMMA showed a homogeneous morphology, whereas those with PET and PVC showed two-phase morphologies. These were accounted for the solubility parameter differences of the polymers. In the case of PVC the mismatch of processing conditions was found to be the main reason for the observed morphology. The technique of FTIR spectroscopy revealed that the relative β-crystal content of PMMA blend reached 70% at 30 wt% PMMA, whereas PET and PVC achieved 80% β-crystals by only 10 wt% modification. This was attributed to the interactions of the blended polymers with PVDF molecules in amorphous regions or at their interphases. The effects of PVC and PET on the beta-crystal content of PVDF are similar although the blends in the case of PET produce finer morphology as compared with those of PVC. It is desirable to find and maximize the content of PVDF in final piezoelectric article. The technique of WXRD shows limited changes in shape and position of PVDF/PMMA and PVDF/PVC blends spectra and considerable changes in shape of PVDF/PET blends spectra. This is found to be related to the amorphous and semi-crystalline structures of PVC and PET, respectively. Due to the spherical symmetry of the PVDF spherulites the piezoelectric coefficient of the blends are found to be zero.

Influence of polymer blending on crystalline structure of polyvinylidene fluoride

Symmetric network poly(vinylidene fluoride) (PVDF) membranes without a dense skin layer were prepared by vapor-induced phase separation from a PVDF/N,N-dimethylacetamide (DMAc)/water system. The effects of evaporation atmosphere, temperature, and humidity during the preparation of the membranes on their morphologies were investigated by scanning electron microscope (SEM). With low temperature and high humidity, the polymer crystallization mechanism dominated the membrane formation process, and the casting solution formed membranes with symmetric morphologies in the vapor phase containing 0.79% DMAc. The effect of additives on the membrane structure and performance was also investigated. The results of adsorption experiments showed that the binding capacity of bovine serum albumin (BSA) increased with the appearance of a circular network morphology and the decrease of mean pore size of the membrane. With the addition of LiCl to the casting solution, the obtained membrane can adsorb BSA up to 150 μg/cm2. Pr...

Preparation of Symmetric Network PVDF Membranes for Protein Adsorption via Vapor-Induced Phase Separation

The high breakdown strength and dipole density in polyvinylidene fluoride(PVDF) suggest potential high energy density achieved in this class of materials, which is highly desirable and even required in many modern compact and high performance electronics and electric systems. However, due to the large remnant polarization, PVDF only exhibits an energy density of ~2–4J/cm3. In this paper, the different approaches to improve and enhance the energy density in this class of materials will be present.

Polyvinylidene Fluoride based polymeric dielectrics for high energy density capacitor application

Polyvinylidene fluoride (PVDF)/poly(tetrafluoroethylene-co-hexafluo-ropropylene) (FEP) blend hollow fiber membranes were prepared by the melt-spinning method. The effects of drawing conditions (drawing ratio and temperature) on the structure and properties of the membranes were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and analysis of membrane morphology. The storage modulus increased with increasing drawing temperature at the same drawing ratio, which improved the membrane's elasticity. The quantity and pore size of the interfacial microvoids both increased significantly with an increase in the drawing ratio at the same drawing temperature. Finally, the membranes were evaluated for their performance in vacuum membrane distillation (VMD). All the membranes had a salt rejection higher than 99.0%.

Effects of post-treatment on the structure and properties of PVDF/FEP blend hollow fiber membranes

Objective: The objective of this study is to examine the characteristics of the research on human vibration in Korea. Background: There have been relatively less interests in vibration than other ergonomic factors in Korea. However, the importance of vibration is increasing as industry and everyday life are more mechanized. Method: This study reports the results of the literature review on the papers about human vibration published in ergonomics-related domestic journals. Results: It was found that more studies have been done on local vibration than on whole body vibration. Diverse topics have been studied in ergonomics community. Conclusion: Further cutting-edge studies are expected than classical safety and health related ones. Application: Some suggestions were proposed hopefully helpful to colleague ergonomists for future research.

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Trend of Human Vibration Research in Korea

코골이 및 수면 무호흡증 등의 수면 질환은 정신적, 육체적 피로감을 유발하고 정상적인 활동에 심각한 영향을 미치고 있다. 코골이는 공기가 좁아진 기도를 통과할 때 진동에 의해서 일어나는 호흡잡음이고, 수면 무호흡은 기도 주변의 조직이 이완됨에 따라 기도가 일시적으로 막히게 될 때 일어나는 현상이다. 이러한 문제를 해결하기 위해 수면 중 코골이를 검출하고 이를 경감하려는 많은 시도가 이루어져왔다. 본 연구에서는 수면 중 코골이 신호의 검출에 있어서 오류가 발생되는 원인인 주변 잡음이나 기타 영향을 제거하기 위한 새로운 센싱 시스템과 분석 알고리즘의 개발을 수행하였다. 센싱 시스템은 베개 내부에 내장되는 두 개의 polyvinylidene fluoride (PVDF) 진동 센서를 포함하고 있으며 검출되는 신호를 수집, 저장하는 하드웨어부와 코골이 신호를 판단하는 신호처리부로 이루어졌다. 베개에 내장되는 PVDF 센서 중 제 1센서는 코골이 신호를 검출하고 제 2센서는 코골이 신호 및 주변의 잡음을 검출한다. 본 실험에는 10명의 피험자가 참여하였으며 수면 중 잡음이 발생할 수 있는 다양한 환경 조건 하에서 신호를 검출하여 분석하였다. 그 결과 다양한 잡음환경 하에서 코골이 신호가 코골이가 아닌 잡음에 비해 약 70% 이상의 에너지 값을 가지는 것을 확인하였고 이를 통해 잡음으로부터 코골이 신호를 정확하게 검출하는 것을 확인하였다. 본 연구의 결과는 수면 중 발생하는 코골이의 경감을 위한 베개의 개발과 정량적인 수면상태 평가를 통해 건강한 수면 환경을 제시할 수 있는 숙면 유도 시스템의 개발에도 활용될 것이다. 【Sleep diseases such as snoring and sleep apnea are physically, mentally harmful and results serious health problems. Snoring, known as breathing noise, is caused by coupled oscillation of the airway when the air passes through the trachea, and sleep apnea is caused by upper airway blockage. In order to solve these problems, many attempts have been made to detect the snoring during sleep and alleviate it. In this study, a new sensing system and analysis algorithm were developed in order to detect snoring sounds correctly under various sleep environments. Two polyvinylidene fluoride (PVDF) vibration sensors were used inside the pillow. The first PVDF sensor detects vibration transmitted through skull caused by snoring. And the second PVDF sensor detects both snoring sounds and ambient noises. The signals of two sensors were acquired through the designed analog circuits, and analyzed for snoring detection. Ten volunteers were participated for the experiment under five different conditions. Data from two PVDF sensors were processed by the established analysis algorithm, and snoring sounds were compared to noises. The results indicated that the energy of snoring is 70% bigger than that of ambient noise, which proves effectiveness of sensing system and analysis algorithm. Further study would be continued for more wide clinical studies with various environment noises. Based on this study, development of anti-snore pillow and sleep monitoring system for comfort sleep could be developed.】

김희선

Papers

Polyvinylidene Fluoride 진동센서를 이용한 코골이 검출

Snoring Detection using Polyvinylidene Fluoride Vibration Sensors