• Composites Research
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• 제28권3호
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• pp.75-80
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• 2015

Poly(vinylidene fluoride-trifluoroethylene; P(VDF-TrFE))는 여러 분야에서 다양한 형태로 활용되고 있는 유망한 전기활성고분자이다. 이 재료는 전기-기계적 특성을 가지고 있기 때문에 다양한 형태의 센서와 구동기로 활용되고 있으며, 복합재료 구조의 거동을 관찰하는 센서로도 활용이 가능하다. 본 논문에서는 세 가지 방법; (1) 전기적 폴링, (2) 어닐링-냉각, (3) 압축을 사용하여 P(VDF-TrFE) 공중합체 필름의 ${\beta}$ 상 결정구조 향상시켜 센서로서의 특성을 강화하기 위한 연구를 수행하였다. P(VDF-TrFE) 필름에 대한 각 방법의 효과를 조사하기 위해 X-선 회절을 통한 미세구조분석을 수행하였다. 실험 결과, 전기적 폴링, 어닐링-냉각, 그리고 압축 방법 모두 P(VDF-TrFE) 필름의 ${\beta}$ 상 결정구조 향상에 효과적이었으며 대조군 (45.29%)대비 최대 62.80%까지 ${\beta}$ 상 결정도가 향상됐다.

• Composites Research
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• 제28권5호
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• pp.270-276
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• 2015

Polyvinylidene fluoride (PVDF)-based nanocomposites are fabricated by incorporation of boron nitride (BN) nanosheets with anisotropic orientation for a potential high thermal conducting ferroelectric materials. The PVDF is dissolved in dimethylformamide (DMF) and homogeneously mixed with exfoliated BN nanosheets, which is then cast into a polyimide film under application of high magnetic fields (0.45~10 T), where the direction of the filler alignment was controlled. The BN nanosheets are exfoliated by a mixed way of solvothermal method and ultrasonication prior to incorporation into the PVDF-based polymer suspension. X-ray diffraction, scanning electron microscope and thermal diffusivity are measured for the characterization of the polymer nanocomposites. Analysis shows that BN nanosheets are exfoliated into the fewer layers, whose basal planes are oriented either perpendicular or parallel to the composite surfaces without necessitating the surface modification induced by high magnetic fields. Moreover, the nanocomposites show a dramatic thermal diffusivity enhancement of 1056% by BN nanosheets with perpendicular orientation in comparison with the pristine PVDF at 10 vol % of BN, which relies on the degree of filler orientation. The mechanism for the magnetic field-induced orientation of BN and enhancement of thermal property of PVDF-based composites by the BN assembly are elucidated.

• 대한방사선기술학회지:방사선기술과학
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• 제27권4호
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• pp.31-35
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• 2004

PVDF[poly(vinylidene fluoride)] 압전소자로 제작된 초음파 변환기를 이용하여 초음파 spectroscopy 측정시스템을 제작하였다. 이 장치를 이용하여 MBBA(p-methoxy benzylidene-p-n-butylaniline) 액정의 nematic-isotropic 상전이 현상을 관측한 결과 상전이 온도가 $47^{\circ}C$임을 확인하였으며, 기존의 광학적 방법에 의해 관측된 값과 잘 일치하였다. 한편으로 상전이 점의 주파수 의존성을 확인하였으나 이는 관측되지 않았으며, 단지 PVDF 압전소자의 공진주파수인 2 MHz에서 초음파의 진폭이 최대로 나타났으며, 다른 주파수에서는 진폭이 감소함을 알 수 있었다. 이와 같이 온도의 변화에 따른 액정의 상전이 현상을 초음파 감쇠의 변화로 확인하여 보았다. 이것은 액정의 상전이 메카니즘을 해석함에 있어 PVDF 초음파 변환기를 이용한 spectroscopy 측정 시스템은 매우 유용한 도구로 이용될 수 있음을 확인하였으며, 의료용으로 이용할 경우 겸상세포 빈혈증이나 동맥 경화증과 같은 질병 진단에 이용 가능하리라 여겨진다.

• 센서학회지
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• 제10권5호
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• pp.320-328
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• 2001

PVDF(Polyvinylidene fluoride) 압전막을 이용하여 $8{\times}8$의 요소를 갖는 2차원 배열 수중청음기를 설계 제작하고. 그것을 이용하여 수 MHz$\sim$수십 MHz 대역의 초음파 음장을 측정하는 방법 및 측정시스템을 구축하였다 수중청음기의 설계에 있어서는 배면체의 종류에 따른 주파수 응답특성을 Mason 등가회로에 의해 해석하였고, 압전체 요소의 크기 및 간격, 스캐닝 스탭에 따른 음장 측정 정도를 검토하였다 2.25MHz의 원형평면 트랜스듀서가 만드는 수중 음장을 제작한 수중청음기 및 측정시스템으로 측정한 결과, 비교적 정밀한 측정이 가능함을 알았다.

• Restorative Dentistry and Endodontics
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• 제27권2호
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• pp.175-182
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• 2002

Dental caries is a chronic disease that causes the destruction of tooth structure by the interaction of plaque bacteria, food debris, and saliva. There has been attempts to induce remineralization by supersaturating the Intra-oral environment around the surface enamel, where there is incipient caries. In this study, supersaturated remineralized solution "R" was applied to specimens with incipient enamel caries, and the quantitative analysis of remineralization was evaluated using microradiography. Thirty subjects volunteered to participate in this study. Removable appliances were constructed for the subjects, and the enamel specimen with incipient caries were embedded in the appliances. The subjects wore the intra-oral appliance for 15 days except while eating and sleeping. The removable appliance were soaked in supersaturated solution "R", saline, or Senstime$^{\circledR}$ to expose the specimen to those solutions three times a day, 5 minutes each time. After 15 days, microradiography was retaken to compare and evaluate remineralization The results were as the following: 1. The ratio of remineralized area to demineralized area was significantly higher in the supersaturated solution "R" and Senstime$^{\circledR}$ than in the saline (p<0.05) 2. Remineralization in the supersaturated buffer solution "R" occurred in the significantly deeper parts of the tooth. compared to the Senstime$^{\circledR}$ group containing high concentration or fluoride. (p<0.05) As in the above results, the remineralization effect of remineralized buffer solution "R" on incipient enamel caries has been proven. For clinical utilization, further studies on soft tissue reaction and the effect on dentin and cementum are necessary In conclusion compared to commercially available fluoride solution. remineralization solution“R”showed better remineralization effect on early enamel caries lesion, so it is considered as effecient solution for clinical application.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.169-170
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• 2006

In this study, ultra thin films of ferroelectric vinylidene fluoride-trifluoroethylene (VF2-TrFE) copolymer were fabricated on degenerated Si (n+, $0.002\;{\Omega}{\cdot}cm$) using by spin coating method. A 1~5 wt% diluted solution of purified vinylidene fluoride-trifluoroethylene (VF2:TrFE=70:30) in a dimethylformamide (DMF) solvent were prepared and deposited on silicon wafers at a spin rate of 2000~5000rpm for 30 seconds. After annealing in a vacuum ambient at $200^{\circ}C$ for 60 min, upper gold electrodes were deposited by vacuum evaporation for electrical measurement. X-ray diffraction results showed that the VF2-TrFE films on Si substrates had $\beta$-phase of copolymer structures. The capacitance on $n^+$-Si(100) wafer showed hysteresis behavior like a butterfly shape and this result indicates clearly that the dielectric films have ferroelectric properties. The typical measured remnant polarization (2Pr) and coercive filed (EC) values measured using a computer controlled a RT-66A standardized ferroelectric test system (Radiant Technologies) were about $0.54\;C/cm^2$ and 172 kV/cm, respectively, in an applied electric field of ${\pm}0.75\;MV/cm$.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2241-2255
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• 2018

RSM methodology was applied to present mathematical models for the fabrication of polyvinylidene fluoride (PVDF) dual-layer hollow fibers in membrane distillation process. The design of experiments was used to investigate three main parameters in terms of polymer concentration in both outer and inner layers and the flow rate of dope solutions by the Box-Behnken method. According to obtained results, the optimization was done to present the proper membrane with desirable properties. The characteristics of the optimized membrane (named HF-O) suggested by the Box-Behnken (at the predicted point) showed that the proposed models are strongly valid. Then, a morphology study was done to modify the fiber by a combination of three types of a structure such as macro-void, sponge-like and sharp finger-like. It also improved the hydrophobicity of outer surface from 87 to $113^{\circ}$ and the mean pore size of the inner surface from 108.12 to 560.14 nm. The DCMD flux of modified fiber (named HF-M) enhanced 62% more than HF-O when it was fabricated by considering both of RSM and morphology study results. Finally, HF-M was conducted for long-term desalination process up to 100 hr and showed stable flux and wetting resistance during the test. These stepwise approaches are proposed to easily predict the main properties of PVDF dual-layer hollow fibers by valid models and to effectively modify its structure.

• 치위생과학회지
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• 제22권3호
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• pp.156-163
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• 2022

Background: This study attempted to apply resin infiltrant (RI) as a method to maintain the effect of tooth bleaching treatment and compared it with fluoride varnish (FV) or artificial saliva to evaluate the effect. Methods: Sixty healthy lozenge specimens were classified into five groups. Group 1 was the negative control group, and discoloration was induced after artificial saliva treatment of the tooth specimen (G1_S+C). Group 2 was a positive control group, in which pigmentation was induced after bleaching treatment and artificial saliva treatment (G2 _B+S+C). Coloration was induced in group 3 (experimental group 1) after bleaching treatment and artificial saliva treatment, followed by application of fluorine varnish (G3_B+FV+S+C). Coloration was induced in Group 4 (experimental group 2) after applying RI after bleaching treatment and artificial saliva treatment (G4_B+RI+S+C). Pigmentation was induced in group 5 (experimental group 3) after bleaching treatment and artificial saliva treatment, followed by acid treatment (etching) and treatment with RI (G5_B+E+RI+S+C). Coffee and wine were used to induce discoloration. The lightness value (L^*) of the CIE L^*a^*b^* color system was obtained by image analysis. Kruskal-Wallis H analysis was performed for the mean difference in L^* values by group. Results: When coloration was induced with coffee, there was no significant difference in L^* value between artificial saliva (G2 _B+S+C), FV (G3_B+FV+S+C), and RI (G4_B+RI+S+C, G5_B+E+RI+S+C) groups. There was no significant difference in L^* values between the artificial saliva (G2 _B+S+C), FV (G3_B+FV+S+C), and RI (G4_B+RI+S+C, G5_B+E+RI+S+C) groups, even in the case of wine induced coloration. Conclusion: It was confirmed that artificial saliva or RI treatment had similar effects to the FV previously used to maintain the effect of tooth bleaching treatment.

• 치위생과학회지
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• 제6권2호
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• pp.55-63
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• 2006

본 연구는 향후 치아우식증 예방을 예방하고 구강건강을 유지 증진시키는데 필요한 기초자료를 제공하고자 하였으며, 김포시 면단위에 소재하는 초등학교 6학년 남 녀 138명을 대상으로 설문지 및 학교 구강검사 결과를 이용하여 우식치아수 및 우식치아수와 관련있는 요인을 조사하여 다음과 같은 결론을 얻었다. 1. 우식치아가 전혀 없는 경우가 응답자의 37.7%로 가장 많았고, '2-3개' 23.9%, '4개 이상' 21%, '1개'는 17.4%이였다. 2. 최근 1년동안 치과의료기관 방문횟수는 1-2회가 52.2%로 가장 많았고, 23.9%는 1년 동안 치과의료기관을 한번도 방문하지 않았다. 3. 하루 평균 잇솔질 횟수에서 2회는 71.7%였고, 54.3%는 잇솔 외 구강관리용품을 전혀 사용하지 않았으며, 86.9%와 71.3%는 각각 치면열구전색과 불소도포 경험이 전혀 없었고, 66.9%는 현재 사용하고 있는 세치제에 불소 배합여부를 전혀 인식하지 못하고 있었다. 4. 우식치아수와 관련있는 사회 인구학적 요인으로는 모친 연령, 모친 최종학력, 모친 취업여부, 하교 후 돌봐주는 사람이었다(p > 0.05). 5. 우식치아수와 관련있는 구강건강행위 요인으로는 하루 평균 잇솔질 횟수, 잇솔 외 구강관리용품 사용, 불소도포 경험이었다(p > 0.05). 6. 우식치아수와 관련있는 간식섭취요인으로는 치아보호식품과 우식성식품 섭취 횟수였다(p >0.05). 7. 우식치아수와 관련있는 구강건강신념항목은 감수성으로 나타났다(p > 0.05). 8. 회귀분석 결과 모친이 미취업이고, 하루 평균 잇솔질 횟수가 많으며, 치아보호식품 섭취횟수가 많고, 우식성 식품섭취가 적으며, 감수성이 낮을수록 우식치아수가 적은 경향을 보였다. 9. 초등학교 아동들에게 많이 발생되는 치아우식증을 예방하고 조기치료를 하기 위하여 학교 내 구강보건실 설치를 확대하며, 집단 구강검사를 통해 구강병을 초기단계에서 발견하여 치료로 연결시키고, 잇솔질 교습 및 불소용액 양치, 식이조절 등이 추진되어야 할 것이다.

• 구강회복응용과학지
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• 제32권1호
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• pp.16-23
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• 2016

목적: 이번 연구는 다양한 pH의 불소 제재들이 티타늄 표면 거칠기에 미치는 영향을 평가하는 것이었다. 연구 재료 및 방법: 기계절삭형 티타늄 디스크를 시중에서 유통되는 세 가지 불소겔로 처리하였다. 불소겔의 종류와 처리 시간에 따라, 대조군, 1군(pH 3.5의 APF로 1분간 처리), 2군(pH 3.5의 APF로 30분간 처리), 3군(pH 4.0의 APF로 1분간 처리), 4군(pH 4.0의 APF로 30분간 처리), 5군(pH 7.0의 NaF로 1분간 처리), 6군(pH 7.0의 NaF로 30분간 처리)의 7군으로 분류하였다. 디스크의 표면 거칠기를 측정한 후, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum을 배양하여 디스크에 부착하는 세균의 양을 측정하였다. 결과: 표면 거칠기는 그룹2에서만 유의하게 증가하였다(P < 0.0001). 세균의 부착량은 실험군과 대조군 사이에 유의한 차이를 보이지 않았다. 결론: pH 3.5의 APF를 30분간 처리한 그룹에서 표면 거칠기가 유의하게 증가하였지만, 세균의 부착에 대해서는 유의한 차이를 보이지 않았다.