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Haq, Muhammad Refatul,Kim, Young Kyu,Kim, Jun,Ju, Jonghyun,Kim, Seok-min IOP 2019 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.29 No.7
<P>A glass microfluidic device with superior chemical and mechanical resistance was fabricated using a cost-effective glass molding process with a vitreous carbon (VC) mold, which was prepared by the carbonization of a replicated polymer precursor. For the development of microfluidic chips with dense microchannels on a large footprint, a defect-free VC mold is essential. In this study, a furan imprinting process, in which a patterned furan layer was imprinted (cured) on a polished furan plate, was established to minimize warpage and gas bubble defects. In addition, the proposed imprinting process markedly reduced the fabrication time of the furan precursor. For feasibility testing, a glass micromixer with a total channel length of 30.6 cm and footprint of 20 × 20 mm<SUP>2</SUP> was developed by glass molding with the VC mold and thermal fusion bonding. The fabricated glass-molded micromixer was durable at an internal pressure of ~24 MPa, and there was no swelling when used with toluene for an extended time.</P>
Development of shrinkage model of micro structured vitreous carbon mold for glass molding
Muhammad Refatul Haq,김준,주종현,김영규,장우진,김석민 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.12
Carbonization of replicated furan precursors has been proposed as a low-cost large-area method for fabricating microstructured vitreous carbon (VC) molds to glass micromolding. During the carbonization of furan precursors, large anisotropic shrinkage occurs inherently owing to thermal decomposition of the material, and this anisotropic shrinkage should be compensated to obtain the designed profiles of microcavities on the VC mold. In this study, a linear gradual shrinkage ratio model (LGSRM) was developed to predict the anisotropic shrinkage characteristics associated with the fabrication of microstructured VC molds. To verify the shrinkage model, the shape change of the VC mold according to the LGSRM was simulated with ANSYS and compared with the experimental results. To determine the coefficients of LGSRM, a finite element analysis code, in which a gradual shrinkage ratio can be assigned to each individual mesh, was developed, and the coefficients of LGSRM were selected to minimize the errors between the simulated and measured geometrical properties of the VC mold.
Solid-State Nanopore for Molecular Detection
Muhammad Refatul Haq,Bong Jae Lee,Jungchul Lee 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.12
Solid-state nanopore (SSNP) or synthetic nanopore using semiconductor materials have established themselves as a single molecule bio-detection platform. Although biological nanopore with fixed dimension has been successfully utilized for many sensing applications, SSNP has unique characteristics of distinctly potent geometries and relaxation of modification. The most common method of molecular detection is to measure the temporal variations of the ionic current in the pore. In this review, the principles of the SSNP and the improvement of device performance for the molecular detection platform are discussed elaborately. Moreover, different experimental aspects of the SSNP are discussed in detail. For instance, the enhancement of spatial resolution, modification of temporal resolution with the difficulties of its analyte-detection, as well as reduction of the electrical noise for the improvement of device sensing functionalities, all are addressed in designated chapters for better conception. In addition, the typical and updated applications of SSNP including DNA, protein and virus are briefly discussed. Finally, this article offers the context needed to comprehend current research trends and promote molecular sensing through synthetic nanopores.
Jun Kim,Seongmin Lee,Md. Ali Asgar,Muhammad Refatul Haq,Seok-min Kim 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.2
Micropatterned glassy carbon (GC) has been introduced as a mold for the metal micro-forming owing to its excellent hot hardness. However, the durability of the mold is a crucial matter for industrial adoption of the technology because the micropattern can be easily damaged due to the thermal shrinkage of the metal workpiece. In this study, we fabricated a GC mold with filleted-micropost pattern by utilizing spin-coating to enhance the durability of the mold. As a result of the molding tests, the filleted-micropost pattern demonstrated excellent durability compared to the bare micropost pattern with sharp corners. Because its smooth surface profile not only reduces stress concentration, but it induces the natural release of the mold from the formed metal, which occurred during the cooling stage. Finally, we confirmed that the proposed method can improve the thermal efficiency of heat exchangers, because the pool boiling performance of the micro-formed AA5052 surface showed 34% and 102% enhancement in critical heat flux and maximum heat transfer coefficient, compared with that of the smooth surface, respectively. The proposed method can be a breakthrough to address the limitations of conventional microfabrication processes to facilitate low-cost and environment-friendly mass production.