(The) structural design and characterization of porous materials with selective pore morphology via novel 3D additive manufacturing strategies

최원준 Graduate School, Yonsei University 2022 국내박사

다공성 소재는 밀도가 있는 물질에 기공을 포함하고 있는 것으로, 이 기공으로 인해 나타나는 다양한 특징이 있습니다. 표면과 내부 기공을 가진 다공성 재료는 기공 구조, 높은 비표면적, 기공률, 기능성 등의 특징을 가지며, 기공 구조가 없는 밀도가 높은 재료보다 특수한 물성을 지니고 있다. 내외부에 존재하는 기공 구조 차이로 인해 단열재, 필터소재, 차량 내부 폼, 의료용 소재 등의 다양한 분야에서 적용 되고 있다. 기공 특성의 퍼포먼스는 기공 사이즈, 분포, 기공률 및 기공 형태에 영향을 미치며, 어느 특정 형태를 갖는 기공구조체가 가장 우수하다 라고 표현하기는 어렵다. 예로서 열린 기공 형태를 갖고 있는 다공성 구조체는 세포성장을 위한 스캐폴더로 활용 시 세포 부착이나 성장 측면에 있어 우수한 퍼포먼스를 나타내지만, 단열특성이 필요한 건축소재로 활용되었을 경우 기공의 특성에 따라 단열 효과의 미흡하고 기계적 강도가 매우 낮기 때문에 적합한 기공의 형태가 아님을 알 수 있다. 이와 반대로 닫힌 기공을 갖고 있는 다공성 소재는 단열 효과는 뛰어날지라도 스캐폴더로 활용 시 열린 기공을 갖고 있는 소재보다는 낮은 세포성장을 갖는다. 이러한 예와 같이 다공성 소재는 활용하고자 하는 최종 결과물에 따라 요구되는 기공의 특성이 확연히 다르기 때문에 원하는 소재를 이용하여 기공의 크기, 분포, 기공형태, 등과 같은 기공 특성을 제어하는 것이 매우 필수적이다. 따라서 본 연구에서는 다공성 구조체의 기공을 형태를 제어하기 위해서 발포압출공정과 에멀전 템플레이팅 방식을 이용하여 기공을 제어해주었으며, 생분해성 소재 중 하나인 폴리락틱에시드를 원소재로 이용하여 다공성 구조체를 제조하고 기공특성을 제어하는 연구를 수행하였다. 또한 3D 프린팅 기술을 융합하여 원하는 디자인을 갖은 기공 구조체를 성공적으로 제조할 수 있었다. 첫 번째 연구로, 생분해성 고분자인 폴리락틱에시드를 이용하여 닫힌 기공을 갖는 기공 구조체를 압출발포 방식을 이용하여 제조하였다. 일반적으로 발포공정은 열가소성 고분자와 블로잉 에이전트의 혼합을 통해 기공을 도입시켜주는데 원소재의 용융강도가 기공 도입 시 매우 중요한 영향을 미치기 때문에 이를 제어하는 것이 필수적이다. 따라서 상용 폴리락틱에시드의 사슬연장반응을 통해 유변물성을 제어하여 용융강도를 개선시키고, 에폭시 결합 반응을 통해 발포 특성의 향상, 기공의 균일성 등을 부여해줄 수 있었다. 다음으로, 유변물성이 제어된 폴리락틱에시드와 화학적 발포제를 이용하여 기공을 형성시키고 균일한 사이즈의 닫힌 기공 형태를 갖는 다공성 구조체를 제조할 수 있었다. 또한 용융압출모델링 3D 프린팅에 적용을 통해 원하는 형태의 구조물로 인쇄할 수 있었고 이 결과물의 세포테스트를 통해 스캐폴더로의 활용 가능성을 확인해보았다. 두 번째 연구로는 에멀전 템플레이팅 기술을 통해 열린 기공을 갖는 다공성 폴리락틱에시드 구조체를 제조하였다. 또한 광경화 방식의 디지털라이트프로세싱 3D 프린팅을 통해 원하는 형태의 구조물을 성공적으로 인쇄하였다. 이 프린팅 방식에 적용시키기 위해서는 광경화 반응을 일으킬 수 있는 작용기가 필수적으로 존재하여야 한다. 따라서 폴리락틱에시드 기반의 소재가 광경화 반응을 수행할 수 있도록 폴리락틱에시드와 글리시딜메타크릴레이트의 공중합을 통해 작용기를 부여해주었으며 가교제와 함께 최적의 레진을 제조하여 프린팅 소재로 적용하였다. 뿐만이 아니라 기공을 도입시켜주시 위해 에멀전 템플레이팅 방식에서 사용되는 오일-인-워터 에멀전 형태로 제조함으로써 상호 연결되어있는 기공을 갖는 기공 구조체를 광경화 중합을 통해 얻어낼 수 있었다. 이외에도 원하는 형태로 인쇄된 다공성 구조물은 기공의 형태 및 소재의 생분해 특성 작용기 유무에 따른 생분해 거동을 효소 분해 공정을 통해 확인해 보았다. 결과적으로, 고전적인 다공성 소재 제조 방식과 신규 3D 프린팅 방식의 기술을 융합하여 기공 특성을 제어하는 연구를 수행하였다. 용융압출발포 공정, 에멀전 템플레이팅 방식을 3D 프린팅을 이용하여 구현함으로써 원하는 구조물형태로 제조할 수 있었으며 기공의 형태를 선택적으로 제어할 수 있었다. 또한 제조된 다공성 구조체의 기공 형태에 따른 세포성장 테스트 및 기공 구조에 따른 생분해 거동을 실험적으로 확인해 봄으로써 생체 적용 스캐폴더 소재로서의 활용 가능성을 확인해보았다. 필요로 하는 기공의 특성을 선택적으로 제어할 수 있는 것과 원하는 구조물 형태로 제조할 수 있는 점은 다공성 소재의 활용성 측면에서 큰 장점을 부여해줄 수 있을 뿐만 아니라 생분해성 소재를 이용함으로써 친환경소재 및 생체 적용 소재로의 활용 가능성을 확인하였다. Porous materials contain pores in dense materials and have various characteristics that are manifested by these pores. A porous material with surface and internal pores has characteristics such as a pore structure, a high specific surface area, a porosity, and functionality, and has special physical properties than a dense material having non porous structure. Due to the difference in pore structure existing inside and outside, it is applied in various fields such as heat insulating materials, filter materials, vehicle internal foams, and medical materials. The performance of pore properties affects pore size, distribution, porosity and pore morphology, and it is difficult to say that a pore structure with a particular morphology is the best. As an example, a porous structure having an open pore morphology shows excellent performance in terms of cell adhesion and growth when used as a scaffold for cell growth. Whereas, it has an unsuitable pore shape to show the heat insulating effect when used as a building material that requires heat insulating properties. On the contrary, a porous material having closed pores has an excellent heat insulating effect, but has lower cell growth than a material having open pores when used as a scaffold. Since these porous materials have distinctly different pore characteristics depending on the final product to be utilized, it is very important to control the pore properties such as pore size, distribution, and pore shape using the desired material. Therefore, in this study, in order to control the pore property as morphology, porous structure, the pores are controlled using the foam extrusion process or the emulsion templating method. Also the porous material with biodegradable property was made using one of the biodegradable materials, polylactic acid. In addition, porous materials with on-demand design was successfully fabricated by combine novel 3D printing to control pore property. In the first content, a biodegradable polymer, polylacticacid, was used to produce a pore structure with closed pores using the extrusion foaming method. Generally, the foaming process introduces pores through a mixture of a thermoplastic polymer and a blowing agent, but it is essential to control this because the melt strength of the raw material has a very important effect on the introduction of pores. Therefore, it was possible to control the rheological property by the chain extension reaction of the commercial polylacticacid to improve the melt strength. Consequently, to improve the foaming characteristics and impart the uniformity of the pores by the epoxy extension reaction. Next, porous materials was produced using polylacticacid with controlled rheological properties and chemical foaming agent, and a porous structure having a uniform size and closed pore morphology. In addition, by applying it to fused deposition modeling 3D printing, it is possible to print with a structure of a desired form, and we confirmed the possibility of using this result as a scaffold through in vitro cell assay. In the second content, emulsion templating technology was used to produce porous polylacticacid structures with open pores. Further, the structure of the desired form was successfully printed by the photocuring digital light processing 3D printing. In order to apply to this printing method, there must be essentially a functional group capable of a photocuring reaction. Therefore, a functional group was imparted by copolymerization of polylacticacid and glycidyl methacrylate so that the polylacticacid-based material could undergo a photocuring reaction. And an optimum resin was produced together with a cross-linker and applied as a 3D printing material. Furthermore, by producing in the form of an oil-in-water emulsion used in the emulsion templating method to introduce pores, a pore structure with interconnected pores could be obtained by photocuring polymerization. Also, in the porous structure printed in the desired form, the biodegradation behavior depending on the morphology of the pores and the presence or absence of the biodegradation characteristic functional group of the material was confirmed through the enzymatic degradation experimental. As a result, we conducted research to control pore characteristics by combine conventional techniques for porous material manufacturing method to the new 3D printing method. By implementing using 3D printing the melt extrusion foaming process or the emulsion templating method, it was possible to produce in a desired structural form, and it was possible to selectively control the pore morphology. In addition, the biodegradation behavior according to the pore shape and pore structure of the porous structure was verified. Also, the effect of cell growth was investigated through a cell growth test, and it was confirmed that it can be used as a scaffold. The novel 3d printing method to selectively control the required pore characteristics and the ability to manufacture in the desired structural form not only provide a great advantage in terms of the utilization of porous materials. Besides we confirmed the possibility of using it for environment-friendly materials and bio-applicable materials by using biodegradable materials.

Modification of Porous Materials for Various Applications

Joseph, Elizabeth Ann Texas A&M University ProQuest Dissertations & Thes 2020 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

In recent years, there has been a rising interest in the field of highly-porous materials. Porous materials come in a large variety of subtypes, allowing for very high levels of versatility and tunability. Porous materials can include both organic and inorganic materials, such as polymers, mesoporous silica, zeolites, covalent organic frameworks (COFs) and metal-organic frameworks (MOFs). These materials often have varying pore sizes, beginning at the nano-scale and extending to visually discernable pore openings. While a sizable portion of scientific research has focused on the development of novel porous materials with increasingly favorable properties, a significant portion of these porous materials have yet to find niche applications outside the laboratory. While many scientifically exciting discoveries perform admirably on the lab scale, going to bulk scale often comes with many challenges that do not present significant issues at smaller scales. Additionally, the syntheses of many porous materials, such as COFs and MOFs, are subject to very specific conditions, with minor changes in these procedures leading to an absence of product formation. As such, the work in this dissertation primarily focuses on materials with existing bulk production procedures, specifically discussing the modification of such materials to provide favorable properties that can then be applied to large scale production.

Crystallographic studies on the interactions between porous and metallic materials and volatiles under high-pressure and high-temperature environments

최진혁 Graduate School, Yonsei University 2023 국내박사

Volatile species such as H2O and CO2 engage in various physical and chemical interactions with solid counterparts to alter their chemical compositions, crystal structures, and other related properties. Here, X-ray diffraction under tightly constrained environments was performed to monitor the interactions of porous materials and metallic Fe with H2O and/or CO2 under controlled pressure and temperature conditions. For porous materials, we investigated a NAT-type zeolite (mesolite) and synthetic framework materials (ZIF-8 and CAU-10-H) under volatile media of H2O, CO2, CHClF2 or SF6. We observed their structural voids to be filled by volatiles as a function of pressure up to respective saturation limits. In the case of mesolite, structuration of absorbed water molecules was observed at increasing pressure up to 1.5 GPa where two types of void-saturated pores became indistinguishable. In the case of synthetic CAU-10-H, similar void-filling of water molecules was observed up to ca. 4 GPa which led to symmetry change by re-distribution of inserted water molecules. In the case of ZIF-8, asymptotic absorption of volatiles was observed regardless of their types, allowing storage of gases with their density comparable to the liquid state. This led to irreversible absorption of CHClF2 and SF6, signaling possible usages in greenhouse gas capture and storage. On the other hand, reaction between compressed iron and volatiles (H2O, CO2) was induced using X-ray free electron lasers (XFEL) under pressures of ca. 5 and 10 GPa and laser-heating with infrared laser at ca. 50 GPa. In reactions between Fe and volatiles at 5 GPa, wüstite were commonly produced with reduced gas species (H2, CO). In reactions at 10 GPa, on the other hand, hydrogen of H2O irreversibly incorporated into the structure of Fe, forming γ-FeHx, with x reaching up to ca. 0.82. These results imply possible formation of reduced atmosphere at the post-giant impact magma ocean of the Earth’s surface. In addition, infrared laser-heating and subsequent decompression experiments at ca. 50 GPa showed that the net oxidation number of iron at the reaction spots decreases as the pressure increases. This allows us to present an early Earth model in which an oxidized upper mantle and a reduced lower mantle are generated based on a depth of approximately 200-305 km inside the Earth after the giant impact. Furthermore, the development of 4th generation XFEL allows X-rays to function not only as a simple probe source, but as a pump source stimulating the material to high pressure and temperature conditions. This implies possible expansion of crystallographic studies from two-variable (pressure and temperature) to three-variable (pressure, temperature and time) experiments. 물과 이산화탄소와 같은 휘발성 물질은 다른 고체 및 액체 상태의 반응물과의 물리-화학적 상호작용을 통해 반응물이 되는 물질의 화학 조성, 결정 구조와 같은 물성을 변화시킨다. 본 연구에서는 다공성 물질 및 철을 반응물로서 물과 이산화탄소를 비롯한 휘발성 물질과 밀봉하여 온도 및 압력을 조절한 상태에서 반응시켰으며, 이를 실시간 X-선 회절을 통해 관찰하였다. 다공성 물질의 경우 본 연구에서는 NAT 구조 제올라이트인 메조라이트와, ZIF-8, CAU-10-H와 같은 합성 유기구조체 물질에 대하여 물, 이산화탄소, CHClF2 (R-22 냉매) 및 SF6와의 고온-고압 하에서의 상호작용을 관찰하였다. 다공성 물질은 공통적으로 상승된 압력 하에서 결정 구조 내 공극의 포화상태까지 휘발성 물질의 분자를 포획하였다. 메조라이트의 경우, Na+ 양이온이 포함된 나트로라이트 층과 Ca2+ 양이온이 포함된 스콜레사이트 층이 압력이 증가함에 따라 유입되는 물 분자의 차이로 약 1.5 GPa 이상의 압력에서 층간의 구분이 약해지는 것이 관찰되었다. CAU-10-H의 경우, 4 GPa의 압력까지 물 분자를 구조 내에 흡수하였으며, 압력에 따라 리간드의 움직임에 의해 공극 내 물 분자의 위치가 변화하며 결정 구조가 변화하는 것이 관찰되었다. ZIF-8의 경우, 이산화탄소 및 CHClF2에 대하여 기체 분자의 크기와 무관하게 2 GPa의 압력에서 공극의 부피가 모두 채워졌으며, 압력 제거 후에도 CHClF2에 대한 비가역적 포획이 관찰되었다 한편, 철과 휘발성 물질 간의 반응은 X-선 자유전자레이저 (XFEL) 및 적외선 레이저 가열을 이용하여 이루어졌으며, 초기 지구의 대충돌 이후의 지구 내부 환경 모의를 목적으로 약 5, 10 GPa의 물 및 이산화탄소 환경 하에서 철과의 반응을 관찰하였다. 철과 물, 철과 이산화탄소 간의 반응에서는 반응의 생성물로서 각각 wüstite + H2 및 wüstite + CO 발생하였으며, 10 GPa 하에서만 수소에 대한 철 구조 내로의 비가역적 포획 (γ-FeHx)이 관찰되었다 (x=H/Fe ~0.82). 본 결과는 초기 지구의 대충돌 이후 표층의 마그마 바다에서의 철과 휘발성 물질 간의 반응에 의한 환원성 기체 (H2, CO)의 대기로의 유입을 유추해볼 수 있다. 또한, 약 50 GPa에서의 적외선 레이저 가열 및 감압 실험을 통해 압력에 따라 반응 지점의 철의 총 산화수가 압력이 증가함에 따라 감소하는 것을 확인하였다. 이를 통해 대충돌 이후 지구 내부의 약 200-305 km 깊이를 기준으로 산화 상태의 상부 맨틀과 환원 상태의 하부 맨틀이 생성되는 초기 지구 모델을 제시할 수 있다. 또한 본 연구를 통해 4세대 X-선 자유전자 레이저의 발달을 통해 X-선이 단순한 물질 과학적 측정 선원이 아닌, 물질에 직접적인 열과 압력을 가하는 선원으로 기능하는 것이 가능함에 따라 기존의 3세대 방사광 가속기에서 널리 진행된 물질에 두 열역학적 변수인 압력과 온도를 가한 상태에서의 물질에 대한 결정학적 연구가 시간 변수가 추가된 4세대 X-선 자유전자 레이저를 이용한 실험으로 확장될 수 있음을 확인하였다.

쿠커비트릴 기반의 유기 다공성 물질의 이온 전도 특성과 응용 : Ion Conduction in Cucurbit[6]uril-based Organic Molecular Porous Material and Its Applications

박준혁 포항공과대학교 일반대학원 2015 국내석사

This thesis describes the synthesis, structures and applications of organic porous materials. In our group, they have already demonstrated that structural characteristics having confined 1D-channels in organic porous material can make highly anisotropic proton conduction and containing guest molecules such as water and HCl molecule influence activity of proton conduction. Thus, we investigated and proposed proton conduction mechanism through single crystal X-ray crystallography and 2H-NMR spectroscopy, and organic molecular porous materials applied as solid electrolyte of lithium-ion battery by simple soaking method. In chapter 2, A new type of solid lithium-ion conducting electrolytes prepared by incorporation of Li+ ions into a cucurbit[6]uril (CB[6]) based organic molecular porous solid shows high Li+ ion conductivity (~10-4 S/cm) and mobility (transference number, tLi+ = 0.7 ~ 0.8). In addition, the solid electrolytes show excellent, thermally stable performance even after several temperature cycles. The results described here represent a significant progress in designing and tailoring of a safe and high performing solid electrolyte which can address the existing challenges in lithium ion battery technologies and may bring a new insight into the development of advanced lithium ion battery. In chapter 3, Proton conduction mechanism of an organic molecular porous material was analyzed by 2H NMR spectroscopy and X-ray single crystal structure. Proton conductivity in porous materials is mainly depending on the guest molecules filling the channels of the materials. Organic molecular porous materials comprising cucurbit[6]uril (CB[6]) containing deuterated guest molecules were prepared for temperature?dependent 2H NMR analysis. Line shape analysis and activation energy values calculated from T1 relaxation time allowed developing a proton conduction mechanism model. 2H-NMR spectroscopy in various temperature give a clue of proton motion and magnitude of hydrogen bonding networks inside channels of D2O containing porous CB[6] and protonated water (D3O+) and hydrochloric acid (DCl) containing porous CB[6]. Finally, existence of acid inside channel forms strong hydrogen bonding as proton conduction pathway and effective proton hoping compared to only water containing porous CB[6]. This work presents a state of the art for crystalline porous materials in proton conduction mechanism study.

Study on oil spreading and capillary imbibition into open-cell porous structure

VOTHITONGUYEN 인천대학교 대학원 2024 국내박사

Widespread interest has been focused on a feasible method of creating 3D porous materials with innovative features for cleaning up oil spills. Modifying commercial melamine sponge (MS), which has an inherently porous open-cell structure, combined with biomass-derived carbon is a facile, scalable, and low-cost strategy for fabricating 3D porous materials. Due to its distinct features, MS was chosen for our study. The design of carbonized seaweed and the use of polyvinylidene fluoride (PVDF) as an adhesive agent, combined with the distinct porosity structure of MS, was considered to be the key component in the likely process of rapid oil absorption. We believe that the porous biomass selection and modification strategies would make this absorbent favorable for oil remediation. Because of its countless pores and capillary-driven force of absorption, the carbonized seaweed-coated melamine sponge (CMS) was able to absorb oil quickly and selectively. Determining the promising capabilities of CMS required a thorough examination of its microstructure and behaviors in connection to the special porous structure, mechanical stability, wetting response, and in-depth processing of the high-speed visualization experiment. For the special CMS structure with a unit cell size of 1x1x1 cm, the total volume of oil inside the capillary tube is drawn inward after 56 ms, and the absorption rate is estimated to be around 15,200 LMH without any external power inputs. According to the results, we propose theoretical models to estimate the oil absorption rate as a function of time by continuity of the oil column in the capillary tube based on quantitative analysis of the optically analyzed oil interface phenomena. We first show it is a reliable approach for describing volumetric absorption rate and estimating CMS thickness by visualizing the capillary spreading flow. As oil spills in the marine become more and more of a serious concern, which raises interest in techniques for monitoring and preventing oil spills as well as means to observe how it spreads. A viable strategy based on an optical method with correlations for selected viscous oil/water systems is proposed. The microscopic spreading and oil capillary penetration state of a porous structure based on a modified melamine sponge was studied. Our initial motivation and interest in this issue were to comprehend the connection between the optical behaviors spreading of oil lens and to eventually apply this to infiltrate into a 3D open-cell porous structure. However, research into the mechanisms that underlie the interaction of viscous oils with this particular porous structure is still in development. For a particular viscous oil/water system, a potential technique based on an optical method with empirical relationships is described. This work presents a thorough examination of the complex processes governing how viscous oil lens behave within MS scaffolds. The present work deals with understanding the spreading of a highly viscous oil lens, and capillary imbibition in contact with a porous structure. The use of the microstructure visualization method could be better to analyze the state of the oil spreading and capillary penetration of oil into the porous structure of CMS. Furthermore, an oil lens in contact with the surface of the CMS porous structure is thoroughly characterized by the balance of forces operating to better comprehend the capillary phenomena over an optical approach. From a knowledge of 2 2 / ( )W O W OS g , we can determine the spreading coefficient S. It needs to be pointed out that the oil lens floating on the water surface does satisfy Neumann’s rule as the spreading coefficient of the air-oil-water system is negative ( – 9.8 mN/m), which suggests the ability to form on the water surface a stable oil lens of thickness O = 3.04 mm and radius LR = 38.64 mm after 60 min of spreading test. Furthermore, to better understand the capillary phenomena over a mechanical approach, an oil lens in contact with the surface of CMS porous structure by in-depth visualization is properly defined as the balance of forces acts. Finally, as a proof-of-concept of this approach, we use mechanical methods to determine the equilibrium height of the capillary rise and integrate it into effective material thickness calculations, which are important in oil spill assessment studies. The objective of this dissertation work is fourfold: (i) Inspired by the biomass-derived for modification of MS, tuning carbon material modified commercial sponge toward pragmatic oil spill cleanup (ii) Determine the promising capabilities of CMS required a thorough examination of its microstructure and behaviors (iii) To present a more thorough experimental description of the spreading of viscous oil lens on the water surface and capillary action of oil lens into CMS porous structure, and (iv) To provide a theoretical description that helps to explain some of the observed behavior. Understanding the complicated dynamics of viscous oil lens spreading and capillary imbibition inside MS porous structures is critical for improving and expanding this remediation approach. This research is anticipated to provide tremendous potential strategies for environmental remediation. Keywords: Spreading, Oil/water separation, Capillary, Porous material, Interconnected structure, Oil remediation, Carbon material, Melamine sponge

Multiscale Approach for Predicting the Acoustic Properties of Porous Material

허준 서울대학교 대학원 2024 국내석사

Multiscale Approach for Predicting the Acoustic Properties of Porous Material Jun Heo School of Mechanical Engineering The Graduate School Seoul National University To control noise, porous materials are widely used, possessing both solid and fluid phases. The acoustic energy incident on these materials is dissipated as heat and friction energy through the interaction between two phases of porous materials. Consequently, porous materials exhibit absorption properties and are widely utilized as sound-absorbing materials. To model the absorption performance, an acoustic model is necessary, with the JCAL model being a representative example. To predict the absorption performance of porous materials using this model, acoustic properties are required. These properties can be directly measured or estimated through inverse methods. However, due to the inherent irregularity of porous materials, a number of samples and measurement processes are needed, leading to significant time and workforce. In this study, we investigate a multiscale approach to predict the macroscopic acoustic properties of materials using scanning electron microscopy (SEM) images. To achieve this, we construct a idealized cell structure model (Kelvin cell) and predict the acoustic impedance through numerical simulation of the model. Geometric parameters are measured from SEM images to build the idealized cell structure model. Finally, the feasibility of the multiscale approach is verified using the measured and estimated acoustic properties and absorption performance values. Keywords : Porous material, Acoustic properties, JCAL model Student Number : 2022-27365 다공성 재료는 차량 내부의 소음 저감을 위하여 여러 곳에 사용되며 특히 흡음소재로 널리 사용되고 있다. 다공성 재료의 흡음성능은 음향 모델을 이용하여 예측할 수 있다. 다만 이 모델을 사용하여 다공성 재료의 흡수 성능을 예측하려면 다공성 재료의 음향 물성이 필요 하다. 지금까지 이러한 물성은 직접 측정하거나 역추정법을 통해 도출해 왔다. 그러나 다공성 소재의 재료 자체의 불규칙성으로 인해 많은 샘플과 측정 과정이 필요하여 상당한 시간과 인력이 소요된다. 본 연구에서는 주사 전자 현미경(SEM) 이미지만을 사용하여 소재의 거시적 음향 특성을 예측하는 멀티스케일적 접근법을 연구하였다. 이를 위해 우리는 PU폼 샘플의 SEM 이미지에 기반하여 이상적인 셀 구조 모델 (Kelvi cell)을 구축하고 해당모델의 유동 시뮬레이션 (FEM)을 통해 재료의 음향 물성 및 흡음률을 예측하였다. 마지막으로, 측정된 및 추정된 음향 특성 및 흡수 성능 값들을 사용하여 멀티스케일적 접근법의 타당성을 검증하였다.

Water imbibition through soft porous materials

Sooyoung Chang 서강대학교 일반대학원 2022 국내박사

The thesis presents a combined experimental and theoretical investigation of the dynamics of water imbibition through soft porous materials. Water-absorbing porous materials such as papers and porous hydrogels are widely used in engineering applications. Microfluidic paper-based analytical devices (μPADs) have been emerged as a novel platform for various point-of-care diagnostics. Porous hydrogel materials are widely used for agricultural substrates, hygienic products, drug delivery systems, and microfluidic devices. The Washburn equation has been widely used to describe the dynamics of water imbibition in various soft porous materials, but its prediction of water imbibition speed has been reported to be inaccurate since the solid matrix of soft porous materials absorbs water with swelling, crucially affecting the imbibition dynamics. In this study, based on the experimental observations on water absorption and swelling of paper and hydrogel, we suggest mathematical models for water imbibition through paper channels and porous structures made of hydrogel considering the effects of both absorption and swelling. Our model is in good agreement with the measurements of the water flow rate through paper channels and hydrogel-coated capillary tubes. By introducing parameters that characterize the absorption and swelling of the materials, our model elucidates how the absorption and swelling regulate the capillary flow through the interconnected pores. The results provide not only a theoretical background for understanding the dynamics of capillary flow through soft porous materials, but also new insights into the engineering applications of these materials.

Synthesis of Nanoporous Materials using Block Copolymer/Inorganic Nanomaterials Hybrids and their Applications to Energy Storage

강은애 포항공과대학교 일반대학원 2012 국내박사

While environmental pollution and depletion of fossil resources have been growing serious, energy storage system such as lithium ion batteries (LIBs) and supercapacitors have been especially considered as a power source for next generation of automobile as well as portable electronic devices. Recently, a lot of efforts have been made to satisfy high level performance, providing high energy density, high power density, long cycle lifetime, low cost, safety, light weight and high packing density, etc. Especially, in order to utilize plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs), lithium ion battery with spinel Li4Ti5O12 as an alternative anode material have been considered as a promising candidate due to several important advantages in spite of lower theoretical capacity (Li4Ti5O12 + 3Li+ + 3e-  Li7Ti5O12, 175 mA h g-1) than already commercialized graphite (372 mA h g-1). First, Ti is an abundant element allowing it to be a cost-effective material. Furthermore, LTO exhibits a Li+ insertion/extraction potential of ~1.55 V (vs. Li/Li+). This enables LTO electrodes not to suffer from many critical problems caused by undesirable electrolyte decomposition that occurs at reductive potentials under ~1 V (vs. Li/Li+). The side reactions not only lead to the formation of a solid electrolyte interphase (SEI) film and gas evolution but also result in low coulombic efficiency especially in the first formation cycle due to a significant loss of Li+. LTO is also known to show exceptional durability because of negligible volume expansion/contraction, < 1%, while graphite experiences ~13% volume change during full charge-discharge. However, the major drawback of LTO is that it is electrically insulating (<10-13 S cm-1). Several approaches to improve the electronic conductivity include carbon coating and metal doping. Another approach to overcome low electrical conductivity is to employ nanostructures, as the reduced dimension significantly shortens the electronic path. In addition, the nanostructures also enable facile transport of the electrolyte to the surfaces of electrochemically active materials, resulting in rapid charge transfer reactions due to the high electrode-electrolyte interface area, and short Li+ diffusion paths. Thus there have been many research efforts to develop nano-sized materials for high rate capability electrodes. However, the nano-sized materials suffer from low packing density, resulting in low volumetric density. Furthermore, it is also possible that the nanoparticles may be released from the electrode surface, cross the separator and cause an internal short circuit. To overcome these problems associated with the nano-sized materials, it is desirable to create a conductive and porous matrix for micrometer-sized particles that provides good particle-particle contact. Namely, mesostructured materials with large open pores, which were first synthesized through a self-assembly method for nanocatalysis, are ideal candidates. Here, we simply synthesized a mesostructured spinel Li4Ti5O12(LTO)-carbon nanocomposite with large ( > 15 nm) and uniform pores via block copolymer self-assembly. Exceptionally high rate capability is then demonstrated for Li-ion battery (LIB) negative electrodes. Polyisoprene- block - poly(ethylene oxide) (PI- b -PEO) with a sp2 -hybridized carbon-containing hydrophobic block is employed as a structure-directing agent. Then the assembled composite material is crystallized at 700 °C enabling conversion to the spinel LTO structure without loss of structural integrity. Part of the PI is converted to a conductive carbon that coats the pores of the Meso-LTO-C. The in situ pyrolyzed carbon not only maintains the porous mesostructure as the LTO is crystallized, but also improves the electronic conductivity. A Meso-LTO-C/Li cell then cycles stably at 10 C-rate, corresponding to only 6 min for complete charge and discharge, with a reversible capacity of 115 mAhg−1 with 90% capacity retention after 500 cycles. In sharp contrast, a Bulk-LTO/Li cell exhibits only 69 mAhg−1 at 10 C-rate. The carbon-coated mesoporous structure enables highly improved electronic conductivity and significantly reduced charge transfer resistance, and a much smaller overall resistance is observed compared to Bulk-LTO. Additionally, to achieve further improvement in rate capability of LTO, a mesostructured Nb doped LTO-carbon composite was successfully synthesized through a simple route of block copolymer assembly with inorganic precursors. During heat-treatment at 700 ˚C, the amorphous metal oxide was crystallized to form the spinel LTO structure and part of the polystyrene in block copolymer was converted to an electrical conductive carbon matrix that not only maintained the pores structure but also provided electrical conductivity to the insulating LTO framework. Pore size was calculated to be 15 nm, large enough for facile diffusion of electrolyte to the LTO framework. The excellent electrochemical performance of 1wt% Nb-LTO, with a capacity of 130 mA h g-1 at 10 C and a capacity of ~ 172 mA h g-1 at 0.5 C, is attributed to the outstanding electrical conductivity of the mesoporous nanoarchitecture combined with generation of Ti3+/Ti4+ mixture as charge compensation by doping Nb5+. This self-assembly method employing block copolymers with a sp2-hybridized carbon and sol-gel process of inorganic materials can simply provide effective ways to improve the electrical conductivity of spinel Li4Ti5O12, which is relevant to fabrication of nano-architectures of Li4Ti5O12, introduction of electrical conductive phase (carbon) and doping with aliovalent metal ion into lattices of Li4Ti5O12. On the other hands, recently, it has been shown that thin-film microbatteries (TFBs) and thin-film microsupercapacitors (TFSCs) are needed to power microelectromechanical system (MEMS)-based sensors and actuators or implanted medical devises (IMDs). To achieve a high energy and

Layered TiO2 based-hybrid materials synthesized by soft chemical exfoliation-reassembling techniques and their applications for visible light active photocatalysts

김태우 Graduate School, Yonsei University 2011 국내박사

AMINE-FUNCTIONALIZED HIGHLY POROUS HYBRID MATERIALS FOR OPHTHALMIC DELIVERY

김세나 서울대학교 대학원 2019 국내박사

이 논문은 안용 약물 전달 시스템에 있어 약물 치료 효과를 향상 시키기 위하여 개발된 초다공성 하이브리드 재료의 디자인, 합성, 표면 기능화, 분석 및 평가에 관한 것이다. 안용약물의 효과적인 안구내 전달을 위하여 나노약물전달 시스템이나 주사형 제형 및 삽입형 디바이스 등 다양한 방법이 시도되었으나 제제의 제작과정이 매우 복잡하여 상용화되기 어렵거나 투약 과정이 침습적인 이유로 환자의 순응도가 낮아 실제 임상에 적용하는 것에 어려움이 있었다. 이로 인해 실제 처방되는 안약물은 90% 이상 점안약물로 처방되며 따라서 점안약물의 약물전달효율을 높이기 위한 방안으로 점도를 높이거나 점막부착성 고분자를 혼입하여 약물의 체류시간을 길게 유지하려는 방법이 적용되어 왔다. 그러나 이러한 제형의 전안부 국소 투여는 눈의 깜박임 및 빠른 눈물 순환작용으로 인해 눈의 표면에서 점안제가 신속히 제거될 뿐만 아니라 대부분이 비루관을 통해 배액되기 때문에 낮은 약물 생체 이용률 (5 % 미만) 문제가 있다. 이를 해결하기 위하여, 눈에 국소 점안 약물 전달을 위한 새로운 운반체로서 금속 유기 골격체, NH2-MIL-88(Fe)을 개발하였다. NH2-MIL-88(Fe)는 점막부착성을 갖는 아민그룹을 포함하는 유기리간드와 Fe 이온을 이용하여 수열합성법을 통해 제조되었으며 분말 X 선 회절, 푸리에 변환 적외선 분석, 열 중량 분석, 전자 현미경 및 N2 흡착-탈착 측정으로 구조를 확인하였다. 녹내장 치료약인 브리모니딘을 NH2-MIL-88(Fe)에 담지 하였을 때, 약물이 121.3 µg/mg 탑재되었으며, 탑재된 약물은 입자의 세공을 통해서 서방출형상으로 최대 12 시간 동안 방출되었다. NH2-MIL-88(Fe)/Br의 점막 접착 성은 in vitro 환경에서 뮤신 흡착 실험을 통해 평가 하였고, 토끼를 이용한 동물 실험에서 4 시간이상 전안부에 남아 있었다. 결과적으로, NH2-MIL-88(Fe)/Br은 투여 후 토끼의 안방수에서 장기간에 걸쳐 브리모니딘 농도가 높게 나타났으며, 이는 약물 생체 이용률 및 활성 기간이 임상에서 사용하는 기존 제재인 알파간피 (Alphagan P) 보다 2 배 이상 증가한 결과였다. 따라서, NH2-MIL-88(Fe)은 안구 약물의 향상된 생체 이용률을 제공하는 점안 약물 국소 전달을 위한 유망한 입자임을 확인하였다. 또한, 항염증 약물인 덱사메타손의 점안 국소 전달을 위한 아민기능화 SBA-15 입자 (즉, APS-SBA-15)을 개발하였다. 메조세공을 갖는 SBA-15 은 수열합성을 통해 제작하고 세공을 확보하기 위하여 소성하였으며, 이후 입자의 표면에 아민그룹을 그라프팅하였다. 표면에 도입된 아민으로 인해, 음이온 특성을 갖는 약물인 dexamethasone이 APS-SBA-15의 중형 기공에 68.23 µg/mg의 양으로 효과적으로 삽입되어 DXS@APS-SBA-15를 생성 할 수 있었고, 약물이 입자에서 24 시간 동안 지속적으로 방출되는 것을 확인하였다. In vitro 환경에서 뮤신과의 혼합실험에서 DXS@APS-SBA-15는 점막 접착 성을 나타내었으며, in vivo 실험에서 토끼 눈에 점안하여 관찰한 결과, DXS@APS-SBA-15는 안점막에 부착함으로써 눈 표면에 오래 거주하는 것을 확인하였다. 개발한 DXS@APS-SBA-15는 임상에서 기 사용하는 기존 제형인 Maxidex 제제에 비해 덱사메타손의 생체 이용률이 1.8 배 이상 향상된 결과를 보였다. 이 연구를 통해, 아민기능화 된 금속-유기 골격체, NH2-MIL-88 (Fe) 및 아민기능화 다공성 실리카 입자, APS-SBA-15가 점막접착성 갖는 것을 확인하였다. 또한 개발한 입자에 생체이용도가 낮은 안용약물인 브리모니딘과 덱사메타손을 각각 탑재하였을때, 약물의 생체이용도가 약 2배가량 증가한 것을 확인하여 점안 약물 국소 투여 제제의 생체 이용률 향상을 위한 유망한 담체 임을 증명하였다. 본 결과를 토대로 아민기능화 초다공성입자의 안용 약물전달 시스템이 점안국소약물 투여에 효율적인 것을 확인하였으며, 이를 다양한 약물에 적용하여 기존에 잦은 점안이 필요했던 다수의 약물 제제에 있어 약물 투여의 불편함을 극복할 수 있을 것으로 생각한다. 또한 점막부착성 아민기능화 초 다공성 입자는 눈 뿐만 아니라 인체 내 여러 부위에 존재하는 점막을 이용하여 다양한 약물전달 시스템에 적용가능하기 때문에 본 연구를 기반으로 이를 이용한 획기적인 연구가 진행될 수 있기를 기대한다. This dissertation is focused on the design, synthesis, surface functionalization, analysis and evaluation of highly porous hybrid materials to enhance the therapeutic effect of ocular drug delivery systems. Ophthalmologic diseases have long been a challenging issue in the field of drug delivery. Numerous studies have been conducted with the goal of increasing the delivery efficiency of eye drop delivery, which accounts for 90% of ophthalmic drug delivery regimens. Topical delivery of ophthalmic drugs poses the problem of low drug bioavailability (< 5%), as conventional eye drops are cleared rapidly from the surface of the eye due to blinking and rapid tear turnover, mostly drained via the nasolacrimal duct. To enhance ocular drug bioavailability after topical administration to the eye, it is necessary for drug carriers to remain on the eye surface for a longer period. A variety of micro- and nano-particles have been proposed to resolve this issue, among which particles composed of mucoadhesive materials have received a great deal of interest. Mucoadhesive particles are known to adhere to the mucin present on the eye surface, and therefore, have the potential to improve the retention of drugs in the preocular space. To develop topical eye drops using highly porous hybrid materials with mucoadhesive functionality, I propose a metal-organic framework (MOF), NH2-MIL-88(Fe), as a novel carrier for topical drug delivery to the eye. NH2-MIL-88(Fe) particles were prepared via a solvothermal synthesis method and their structure was confirmed by powder X-ray diffraction, Fourier transform infrared analysis, thermogravimetric analysis, electron microscopy, and N2 adsorption-desorption measurements. When brimonidine, an anti-glaucoma medicine, was encapsulated into NH2-MIL(Fe)-88 (i.e., NH2-MIL-88(Fe)/Br), the drug was loaded at 121.3 mg/mg and released in a sustained manner for up to 12 h. The NH2-MIL-88(Fe)/Br exhibited mucoadhesive properties and remained on rabbit eyes for a period of up to 4 h. Consequently, a high concentration of brimonidine was found in tears for a prolonged period after the administration of NH2-MIL-88(Fe)/Br, which resulted in a greater than two-fold increase in drug bioavailability and the activity period compared with those of Alphagan-P, a brimonidine eye drop already approved for clinical use. Hence, NH2-MIL-88(Fe) appears to be a promising carrier for topical delivery to the eye that provides enhanced bioavailability for ocular drugs. I also propose the use of amine-grafted SBA-15 particles (i.e., APS-SBA-15) for topical delivery of dexamethasone to the eye. Owing to the surface functionalization of amine groups, dexamethasone, an anionic drug, can be effectively loaded in the mesopores of APS-SBA-15 at loading quantities of 68.23 µg/mg to yield DXS@APS-SBA-15, which, in turn, can be released in a sustained manner for 12 h. DXS@APS-SBA-15 exhibited pronounced mucoadhesive properties because of the presence of both amine and hydroxyl groups in the particles. Therefore, when administered to rabbit eyes in vivo, the DXS@APS-SBA-15 appeared to adhere to the mucin and stay longer on the eye surface, where the drug could be released slowly. Hence, the DXS@APS-SBA-15 introduced herein resulted in > 1.8-fold improvement in the in vivo ocular bioavailability of dexamethasone compared to the conventional eye drop, Maxidex. Through these studies, I concluded that amine functionalized metal-organic frameworks (MOFs) and amine grafted mesoporous silica particles are promising carriers for enhanced bioavailability of topically-delivered ocular drugs. They are also expected to be widely used in various mucin-rich organs, not limited to ophthalmic drug delivery systems.