• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.9
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• pp.754-760
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• 2008

A two-photon induced photoreduction process suggests a possibility for fabricating complicated metallic microstructures which can be applied to 3-D micro-circuits and optical devices, etc. The process employs the photoreduction of silver ions in a metallic solution which is composed of metallic salt ($AgNO_3$) and watersoluble polymer ((poly(4-styrenesulfonique acid) 18wt. % in $H_2O$, $(C_8H_8O_3S)_n$)). In this process, the improvement of the resolution and the uniformity of fabricated metallic structures are important issues. To address these problems, continuous forming window (CFW) is obtained from a parametric study on the conditions of laser power and scanning velocity and the direct seed generation (DSG) method is proposed. Silver nano particles are uniformly generated in a metallic solution through the DSG method, which enables the decrease of a laser power to trigger the photoreduction of silver ions as well as the increase of metal contents in a metallic solution. So the two-photon induced photoreduction property of a metallic solution is improved. Through this work, precise silver patterns are fabricated with a minimum line width of 400 nm.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.10
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• pp.93-99
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• 2010

A nano-stereolithography is the direct patterning process with a nanoscale resolution using twophoton absorption induced by a femtosecond laser. However, in the majority of the works, the fabrication of 3D microstructures have been done only onto transparent glass due to the use of an oil immersion objective lens for achieving a high resolution. In this work, the coaxial illumination and the auto-focusing system are proposed for the direct patterning of nano-precision patterns on an opaque substrate such as a silicon wafer and a metal substrate. Through this work, 3D polymer structures and metallic patterns are fabricated on a silicon wafer using the developed process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.43-46
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• 2005

Micro molding technology is a promising mass production technology for polymer based microstructures. Mass production technologies such as the micro injection/compression molding, hot embossing, and micro reaction molding are already in use. In the present study, we have developed a numerical analysis system to simulate three-dimensional non-isothermal cavity filling for hot embossing, with a special emphasis on the free surface capturing. Precise free surface capturing has been successfully accomplished with the level set method, which is solved by means of the Runge-Kutta discontinuous Galerkin (RKDG) method. The RKDG method turns out to be excellent from the viewpoint of both numerical stability and accuracy of volume conservation. The Stokes equations are solved by the stabilized finite element method using the equal order tri-linear interpolation function. To prevent possible numerical oscillation in temperature Held we employ the streamline upwind Petrov-Galerkin (SUPG) method. With the developed code we investigated the detailed change of free surface shape in time during the mold filling. In the filling simulation of a simple rectangular cavity with repeating protruded parts, we find out that filling patterns are significantly influenced by the geometric characteristics such as the thickness of base plate and the aspect ratio and pitch of repeating microstructures. The numerical analysis system enables us to understand the basic flow and material deformation taking place during the cavity filling stage in microstructure fabrications.

• Coupled systems mechanics
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• v.11 no.1
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• pp.15-32
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• 2022

The comprehensive understanding of the fiber reinforced polymer behavior requires the use of advanced non-destructive testing methods due to its heterogeneous microstructure and anisotropic mechanical proprieties. In addition, the material response under load is strongly associated with manufacturing defects (e.g., voids, inclusions, fiber misalignment, debonds, improper cure and delamination). Such imperfections and microstructures induce various damage mechanisms arising at different scales before macrocracks are formed. The origin of damage phenomena can only be fully understood with the access to underlying microstructural features. This makes X-ray Computed Tomography an appropriate imaging tool to capture changes in the bulk of fibrous materials. Moreover, Digital Volume Correlation (DVC) can be used to measure kinematic fields induced by various loading histories. The correlation technique relies on image contrast induced by microstructures. Fibrous composites can be reinforced by different fiber architectures that may lead to poor natural contrast. Hence, a priori analyses need to be performed to assess the corresponding DVC measurement uncertainties. This study aimed to evaluate measurement resolutions of global and regularized DVC for glass fiber reinforced polymers with different fiber architectures. The measurement uncertainties were evaluated with respect to element size and regularization lengths. Even though FE-based DVC could not reach the recommended displacement uncertainty with low spatial resolution, regularized DVC enabled for the use of fine meshes when applying appropriate regularization.

• Polymer(Korea)
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• v.30 no.6
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• pp.471-477
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• 2006

Ion exchange metal composite(IPMC) has toughness equivalent to the range of human's muscle, transformation-actuation force by relatively low voltage and the fast response time. Thus, as a new method for preparing thicker IPMC, the solution casting method to make the films of various thicknesses out of liquid nation was attempted in this study. To reduce the surface resistance of electrode, the first plated electrode prepared by Oguro method was replated with Au and Ir using ion beam assisted deposition(IBAD). The microstructures of electrode surfaces before and after IBAD plating were investigated using SEM. The change of water and ion-conductivity in IPMC were measured under applied voltage. The displacement and driving force of IPMCs with various thicknesses were measured to evaluate the driving properties.

• Applied Chemistry for Engineering
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• v.18 no.6
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• pp.580-586
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• 2007

In this study, 4 directional carbon/carbon composites with different preform architectures were manufactured and their thermophysical properties are studied. Carbon fiber preforms are fabricated with fiber bundles using four different spaces. The density of the fabricated preforms were increased through pressure impregnation and carbonizing process. The increased density of the composites was graphitized at $2300^{\circ}C$. Microstructures of these composite were observed under scanning electron microscope. This was to understand the effect the preform architectures has on the thermophysical properties of carbon/carbon composites. Also, the behavior of thermal conduction and heat expansion was investigated and studied in association with the factors of the reinforced direction of fibers and unit cell of preforms.

• Polymer(Korea)
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• v.29 no.2
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• pp.146-150
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• 2005

A nano-stereolithouaphy (NSL) apparatus has been developed for fabrication of microstructures with the resolution of 150 nanometers. In the NSL process, a complicated 3D structure can be fabricated by building layer by layer, so it does not require any sacrificial layer or any supporting structure. A laminated layer was fabricated by means of solidifying liquid-state monomers using two-photon absorption (TPA) which was induced by a femtosecond laser. When the fabrication of a 3D laminated structure was finished, unsolidified liquid-stage resins were removed to develop the fabricated structure by dropping several droplets of solvent, then the polymerized structure was only left on the glass substrate. A microstructure is fabricated by vector scanning method to save the fabrication time. The shell thickness of a structure is very thin within 200 nm, when it is fabricated by a single contour scanning (SCS) path. So, a fabricated structure can be deformed easily in the developing process. In this work, a double contour scanning (DCS) method was proposed to reinforce the strength of a shell typed structure, and a microcup was fabricated to show the usefulness of the developed NSL system and the DCS method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.110-110
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• 2009

Aerosol deposition method(ADM)는 상온에서 에어로졸화된 고상의 원료분말을 노즐을 통해 분사시켜 소결과정을 거치지 않고도 상온에서 고밀도 후막을 제조할 수 있는 공정으로서, 다양한 재료의 코팅이 가능하고, 코팅층의 조성 및 화학 양론비의 제어가 용이한 특징을 갖는다. 본 연구에서는 ADM을 이용하여 큰 유전상수, 압전계수, 초전계수, 탄성계수를 갖는 $BaTiO_3$ 분말을 원료로 하여 압전소자, 커패시터, 고전압용 유전체 등에 응용이 가능한 세라믹 층 형성에 관한 연구를 진행하였다. 또한 $BaTiO_3$ 같은 강유전체 세라믹을 이용하여 여러 가지 소자를 제조하는 경우 소자의 미세조직에 따라 물성이 영향을 받는 것으로 확인되어져 있다. 이에 본 연구에서는 세라믹 분말보다 상대적으로 탄성이 큰 polymer 분말을 첨가하여 후막 내부의 결정립의 크기가 20 nm 의 평균 결정립을 갖는 세라믹 후막에 비해 최대 10 배 정도까지 증가하는 것을 확인할 수 있었으며, 이에 따라 후막에서의 유전율 및 유전손실율의 전기적 특성 변화를 확인할 수 있었고, 이러한 물성변화에 대한 원인 고찰을 위하여 후막의 미세구조 및 화학조성 등에 대한 다양한 분석이 이루어 졌으며, 상온에서 성막되는 후막의 세라믹 층의 응용을 위한 최적의 공정조건을 제시하고자 한다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.294-297
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• 2004

RTP(Rapid Thermal Pressing) is to fabricate desired pattern on polymer substrate by pressing patterned mold against the substrate heated around glass transition temperature. For a successful RTP process, the whole process including heating, molding, cooling and demolding should be conducted 'rapidly' as possible. As the RTP process is effective in replicating patterns on flat large surface without causing shape distortion after cooling, it is being widely used for fabricating various micro/bio application components, especially with channel-type microstructures on surface. This investigation finally aims to develop a RTP process machine for mass-producing micro/bio application components. As a first step for that purpose, we intended to examine the technological difficulties for realizing mass production by RTP process. Therefore, in the current paper, 4 kinds of RTP machines were examined and then the RTP process was conducted experimentally for PMMA film by using one of the machines, HEX 03. The micro-patterned molds used for RTP experiment was fabricated from silicon wafer by semi-conduct process. The replicated micro patterns on PMMA films were examined using SEM and the causes of defect observed in the replicated patterns were discussed.

• Polymer(Korea)
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• v.39 no.2
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• pp.287-292
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• 2015

Characterization of a series of bio-based terpolymers containing various amounts of ethylene glycol, 1,4-cyclohexylene dimethanol, and isosorbide units were studied by $^1H$ NMR and $^{13}C$ NMR. The NMR results revealed that they had all random microstructures and that their sequence distribution was affected by the content of isosorbide. From DSC data for the terpolymer series investigated, it was observed that the glass transition temperature increased mainly as the content of isosorbide increased. The glass transition temperatures of terpolymers were estimated from the composition by extended Fox equation.