• Journal of Pharmaceutical Investigation
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• 제40권4호
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• pp.245-250
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• 2010

Porous poly(lactic-co-glycolic acid) microspheres (PLGA MS) have been utilized as an inhalation delivery system and a matrix scaffold system for tissue engineering. Here, gelatin (type A) is introduced as an extractable pH-responsive porogen, which is capable of controlling the porosity and pore size of PLGA microspheres. Porous PLGA microspheres were prepared by a water-in-oil-in-water ($w_1/o/w_2$) double emulsification/solvent evaporation method. The surface morphology of these microspheres was examined by varying pH (2.0~11.0) of water phases, using scanning electron microscopy (SEM). Also, their porosity and pore size were monitored by altering acidification time (1~5 h) using a phosphoric acid solution. Results showed that the pore-forming capability of gelatin was optimized at pH 5.0, and that the surface pore-formation was not significantly observed at pHs of < 4.0 or > 8.0. This was attributable to the balance between gel-formation by electrostatic repulsion and dissolution of gelatin. The appropriate time-selection between PLGA hardening and gelatin-washing out was considered as a second significant factor to control the porosity. Delaying the acidification time to ~5 h after emulsification was clearly effective to make pores in the microspheres. This finding suggests that the porosity and pore size of porous microspheres using gelatin can be significantly controlled depending on water phase pH and gelatin-removal time. The results obtained in this study would provide valuable pharmaceutical information to prepare porous PLGA MS, which is required to control the porosity.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.478-481
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• 1997

A technique or the preparation of porous polyurethane vascular prostheses was investigated. Small-diameter vessels are not in general clinical use due to their limited long-term biocompatibility and low patency rates in experimental trial. These limits are mainly due to the failure of mechanical unction of the vascular grafts. This failure has been suggested to result partially from compliance mismatch. The long-term patency is considered to depend critically on the properties of the material and the fabrication process of the graft. So the control of pores is very important and main points to develop a available vascular grafts. Two-kind polymer sheets was compared. One was the porous PU-sheet made at room temperature by the solvent/non-solvent exchange. And the other was the porous PU-sheet which was fabricated by thermal phase transition and solvent-/non-solvent exchange using the thermal controller. The polymer sheets had a uniform pore size and pore occupation. According to the result of the above experiments, polyurethane solution was injected into a mold designed or U-type tube. The average pore size and pore occupation were easily changed by changing polyurethane concentration, freezing temperature, and methods. This technique can give a proper pore size ($10{\sim}45\;{\mu}m$) or tissue in growth, and suitable compliances or matching with arteries and veins. Besides, the fabrication of more complicated shaped vessels such as the U-type vascular grafts is easily controlled by using the fixed mold. this method might give a desired compliant graft or artificial implantation with the presently valid medical polymers.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.385-390
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• 2002

Autogenous shrinkage of concrete has been defined as decrease in volume due to hydration cement, not due to other causes such as evaporation, temperature change and external load and so on. For ordinary concretes, autogenous shrinkage is so little compared to the other deformations that it has been dignored. It has recently been proved, however, that autogenous shrinkage considerably increase with decrease in water to cement ratio. And it has been reported that cracking can be caused by autogenous shrinkage, when high- strength concretes were used. In this study, we propose an analytical system to represent autogenous shrinkage in cement paste in order to control crack due to autogenous shrinkage. The system is composed with the hydration model and pore structure model. Contrary to the usual assumption of uniform properties in the hydration progress, the hydration model to refine Tomosawa's represents the situation that inner and outer products are made in cement paste. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste and chemical phenomenon of hydration in cement particle. The proposed model can predict the pore volume ratio and the pore structure in cement paste under variable environmental conditions satisfactorily The autogenous shrinkage prdiction system with regard to pore structure development and hydration at early ages for different mix-proportions shows a reasonable agreement with the experimental data.

• 한국세라믹학회지
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• 제45권2호
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• pp.132-137
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• 2008

The main purpose of this study is enhancing the filtering efficiency, performance and durability of filter by growing SiC whiskers on cordierite honeycomb substrate. The experiment was performed by Chemical Vapor Infiltration (CVI) in order to control pore morphology of substrate. Increasing the mechanical strength of porous substrate is one of important issues. The formation of "networking structure" in the pore of porous substrate increased mechanical strength. The high pressure gas injection to the specimen showed that a little of whiskers were separated from substrate but additional film coating enhanced the stability of whisker at high pressure gas injection. Particle trap test was performed. More nano-particle was trapped by whisker growth at the pore of substrate. Therefore it is expected that the porous cordierite which deposited the SiC whisker will be the promising material for the application as filter trapping the nano-particles.

• Carbon letters
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• 제13권4호
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• pp.236-242
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• 2012

Poly(vinylidene chloride) (PVDC)-derived nanoporous carbons were prepared by various activation methods: heat-treatment under an inert atmosphere, steam activation, and potassium hydroxide (KOH) activation at 873, 1073, and 1273 K. The pore structures of PVDC-derived nanoporous carbons were characterized by the $N_2$ adsorption technique at 77 K. Heat treatment in an inert atmosphere increased the specific surface area and micropore volume with elevating temperature, while the average micropore width near 0.65 nm was not significantly changed, reflecting the characteristic pore structure of ultramicroporous carbon. Steam activation for PVDC at 873 and 1073 K also yielded ultramicroporosity. On the other hand, the steam activated sample at 1273 K had a wider average micropore width of 1.48 nm, correlating with a supermicropore. The KOH activation increased the micropore volume with elevating temperature, which is accompanied by enlargement of the average micropore width from 0.67 to 1.12 nm. The average pore widths of KOH-activated samples were strongly governed by the activation temperature. We expect that these approaches can be utilized to simply control the porosity of PVDC-derived nanoporous carbons.

• 한국세라믹학회지
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• 제43권9호
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• pp.564-568
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• 2006

AlO(OH) nano gel is used in precursor of ceramic material, coating material and catalyst. For use of these, not only physiochemical control for particle morphology, pore characteristic and peptization but also studies of synthetic method for preparation of advanced application products were required. In this study, AlO(OH) nano gel was prepared through the aging and drying process of aluminum hydroxides gel precipitated by the hydrolysis reaction of dilute NaOH solution and aluminum sulfate solution. In this process, optimum synthetic condition of AlO(OH) nano gel having excellent pore volume as studying the effect of water and aluminum sulfate mole ratio on gel precipitates has been studied. Water and aluminum sulfate mole ratio brought about numerous changes on crystal morphology, surface area, pore volume and pore size. Physiochemical properties were investigated as using XRD, TEM, TG/DTA, FT-IR, and $N_2$ BET method.

• Korean Chemical Engineering Research
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• 제60권4호
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• pp.557-563
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• 2022

극세 공극 직물의 알레르겐 투과율을 측정하기 위해서는 극세 공극 직물의 공극을 측정하는 편리하고 적절한 실험 장치의 연구 개발이 필요하다. 본 연구에서는 중량 감소율을 측정하여 극세 공극 직물의 공극 크기를 측정하기 위한 간단하고 경제적인 실험 방범을 개발하였다. 또한, 개발된 미세 입자 투과 장치를 사용하여 다양한 직물의 공극 크기를 측정하여 알레르겐 차단 성능을 평가하였다. 본 연구에 의하면 극세 공극 직물의 공극의 크기는 중량 감소 비율을 측정함으로써 구할 수 있었다. 또한 중량 감소 비율의 값은 입자 투과 장치를 통과하는 흡입 압력이 작을수록, 흡입 시간이 길수록 큰 값을 나타났으며, 이 값으로부터 직선 삽입 방법을 통하여 실험 직물의 공극 크기를 측정 할 수 있었다. 개발된 실험 장치 및 방법은 집먼지 진드기 차단 침구에 사용되는 극세 공극 직물에 대하여 그 효과를 검증하는 품질 관리 방법의 실험 기준으로 사용될 수 있을 것으로 기대된다.

• 한국지반공학회논문집
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• 제23권6호
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• pp.77-84
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• 2007

유입량과 라이닝에 작용하는 간극수압은 터널 설계시 고려해야 할 중요한 요소 중 하나이다. 간극수압의 발생은 누수를 가속화시키며 라이닝 열화를 초래한다. 본 논문에서는 모형실험을 통하여 배수시스템 기능저하로 인한 간극수압의 발생과 그 영향을 조사하였다. 배수시스템 기능저하거동은 배수재의 투수계수제어법과 유량 조절법으로 모사화 하여 터널 라이닝의 잔류수압발생 메카니즘을 확인하였다. 또한, 유량제어법이 배수시스템 기능저하현상을 모사하기에 보다 더 효과적인 방법임을 알 수 있었다. 모형실험을 수치해석으로 재현한 결과, 배수시스템 기능저하로 인한 영향을 Coupled 수치 모델링을 통해 이론적으로 예측 가능함을 확인할 수 있었다.

• 한국물환경학회지
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• 제24권6호
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• pp.793-800
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• 2008

Recently domestic drinking water industry has recognized membrane-based technology as a promising alternative for water treatment. To ensure successful application of membrane processes, the integrity of membrane systems should be maintained. According to US EPA guidance, the pressure decay test based on the bubble point theory is recommended to detect any membrane defection of which size is close to the smallest diameter of Cryptosporidium oocysts, $3{\mu}m$. Proper implementation of the pressure decay test is greatly affected by initial test pressure, and the interpretation of the test results is associated with upper control limit. This study is conducted to investigate various factors affecting determination of initial test prtessure and upper control limit, including membrane-based parameters such as pore shape correction factor, surface tension and contact angle, and system-based parameters, such as volumetric concentration factor and total volume of system. In this paper, three different hollow fibers were used to perform the pressure decay test. With identical initial test pressure applied, their pressure decay tendency were different from each other. This finding can be explained by the micro-structure disparity of those membranes which is verified by FESEM images of those membranes. More specifically, FESEM images revealed that three hollow fibers have asymmetry, deep finger, shallow finger pore shape, respectively. In addition, sensitivity analysis was conducted on five parameters mentioned above to elucidate their relation to determination of initial test pressure and upper control limit. In case of initial pressure calculation, the pore shape correction factor has the highest value of sensitivity. For upper control limit determination, system factors have greater impact compared to membrane-based parameters.

• 한국분말재료학회지
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• 제22권4호
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• pp.240-246
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• 2015

Anodic aluminum oxide (AAO) has been widely used for the development and fabrication of nano-powder with various morphologies such as particle, wire, rod, and tube. So far, many researchers have reported about shape control and fabrication of AAO films. However, they have reported on the shape control with different diameter and length of anodic aluminum oxide mainly. We present a combined mild-hard (or hard-mild) anodization to prepare shape-controlled AAO films. Two main parameters which are combination mild-hard (or hard-mild) anodization and run-time of voltage control are applied in this work. The voltages of mild and hard anodization are respectively 40 and 80 V. Anodization was conducted on the aluminum sheet in 0.3 mole oxalic acid at $4^{\circ}C$. AAO films with morphologies of varying interpore distance, branch-shaped pore, diameter-modulated pore and long funnel-shaped pore were fabricated. Those shapes will be able to apply to fabricate novel nano-materials with potential application which is especially a support to prevent volume expansion of inserted active materials, such as metal silicon or tin powder, in lithium ion battery. The silicon powder electrode using an AAO as a support shows outstanding cycle performance as 1003 mAh/g up to 200 cycles.