Effect of Gd-alloyed Neutron Absorber on Thermal Performance of a Spent Fuel Cask

Hee-Jae Lee Graduate School of UNIST 2017 국내석사

A spent fuel cask must be designed to provide safety functions. In particular, in order to maintain the sub-criticality safety, different neutron absorbers have been used for the spent nuclear fuel management system. Although BORAL is the most used neutron absorber, several problems have been reported and it has some potential problems for long term storage of spent nuclear fuels. Recently, a Gd-alloyed duplex stainless steel demonstrated the possibility of fabrication and under development for an advanced neutron absorber and structural material as well. In this study, the effect of Gd alloyed neutron absorber on thermal performance of a spent fuel cask has been studied. The thermal properties of Gd-alloyed DSS was measured using the specimens provided by KITEC. The effect of Gd-alloyed duplex stainless steel adoption was analyzed for the reference casks, KSC-1 and KORAD-21. The analysis method was verified by comparing the analysis results with the reported values. Their system with Gd-alloyed DSS should remove decay heat with passive cooling. The KSC-1 and KORAD-21 casks were modeled with a 2D axis-symmetry condition and 3D symmetry condition, respectively, using ANSYS FLUENT v17.0. Based on the verified method, thermal performance of KORAD-21 which adopts Gd-alloyed DSS was analyzed. The maximum fuel cladding temperature with Gd-alloyed DSS exceeded allowable temperature of 400 ℃ and it could affect the fuel integrity. Therefore, basket wall thickness and disk thickness were optimized to enhance thermal performance. When the basket wall thickness was reduced, the gap between the basket surface and disk square holes was consequently increased. The increased gap enhanced the upward flow of helium and it improved the decay heat removal. Additionally, disk thickness was optimized to 60mm from 20mm. The increased heat-conducting surface enhanced the conduction heat transfer. As a result, UNIST-version design of the KORAD-21 cask was developed with the 5.0mm basket wall thickness and 60mm disk thickness. Thermal performance of UNIST design cask satisfied thermal requirements in normal operation.

Development of New Earth System Model and Investigation of the Impacts of Vegetation on Hydrological Cycle Using Developed ESM

Dongmin Kim Graduate School of UNIST 2017 국내박사

This thesis is to develop a version of the earth system model (ESM) with the interactive vegetation parameterization scheme and investigate the influences and feedback processes driven by terrestrial vegetation on climate and global hydrological cycle. Previous observation and modeling studies suggested that the temporal variation of atmospheric CO2 concentration depends largely on the carbon uptake by terrestrial biosphere, compared with that by oceanic counterpart. In the state-of-the-art ESMs, the parameterization uncertainty in the carbon cycle between land and atmosphere is still large, which tend to produce a significant spread in the model simulations for the ambient CO2 amount and its secular trend. The huge spread of CO2 in turn causes a wide spread in the simulated climate through vegetation-climate feedbacks, which make their future climate projection less accurate and less reliable. One aspect of the parameterization uncertainties lies in the nitrogen process, a critical process coupled with the carbon cycle by limiting supplement of nutrients both to subsurface soil organic matter (SOM) and plants at the surface, which is either absent or represented poorly in current ESMs. A few ESMs with a primitive version of the carbon-nitrogen (C-N) coupling exhibit a significant model deficiency such as the underestimation in the carbon pools or storages in the vegetation and sub-surface soil systems and substantially weak carbon uptake, whereas the other models without C-N coupling tend to overestimate them. The interaction and feedbacks between vegetation and climate should be, therefore, understood based on a more improved understanding of the C-N cycle and its representation in the ESMs. Before developing new ESM, the model intercomparision using 11 CMIP5 ESMs has been done first to evaluate the overall representation of the terrestrial biogeochemical cycle and the model dependences. Using the MODIS satellite estimates, the study validates the simulation of gross primary production (GPP), net primary production (NPP), and the carbon use efficiency (CUE) depending on plant function types (PFTs). The models show noticeable deficiencies from MODIS in the simulation of horizontal patterns of GPP and NPP as well as large simulation differences, although their multi model ensemble (MME) mean represents realistic global mean value and the spatial distributions. Larger model spreads in GPP and NPP than those in surface temperature and precipitation suggest that the simulation difference in terrestrial carbon cycle is largely attributed to the uncertainties in the dynamic vegetation model parameterizations. The models also exhibit large differences in the simulation for CUE geographically and at the change of dominant PFTs, primarily due to the differences in parameterization. While the MME of CUE shows strong dependence on surface temperature, the observed CUE from MODIS shows more complex and non-linear sensitivity. To developing new ESM, this study uses the Geophysical Fluid Dynamics Laboratory Earth System Model version 2 (GFDL-ESM2M) as a base model for the further development. GFDL-ESM2M has a full capability of interactive vegetation parameterizations, and with decent simulations in the long-term climatology and climate variability compared with other ESMs in the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5). The model has comprehensive carbon cycle both for the terrestrial and aquatic environments, yet with no C-N coupling. In order to implement the C-N cycle in the model, this study replaces the Land Model version 3 of GFDL-ESM2M with the Community Land Model version 4 (CLM4). The latter land model is the most recent version in the development suits by NCAR, with more detailed vegetation types and biogeochemistry as well as the interactive C-N parameterizations. However, the Community Earth System Model (CESM) with CLM4 has a well-known bias of the pronounced underestimation in the terrestrial carbon uptake. This is one of the major motivations in this research. The developed ESM named as UNIST-ESM shows the reasonable simulation skill for climate conditions and terrestrial carbon fluxes. The features of distribution of carbon cycle is depended onto land surface models and the features of spatial distribution of climate conditions is dominant to characteristics for atmospheric model in UNIST-ESM. In terrestrial carbon cycle, UNIST-ESM still has systematic bias for simulating GPP in the globe. The underestimation (overestimation) of GPP over high latitude region (tropics) in UNIST-ESM is major deficiencies of simulation of terrestrial carbon cycle. For improvement of deficiencies of terrestrial carbon cycle in UNIST-ESM, this study develops a new parameterization method for determining Q10 by considering the soil respiration dependence on soil temperature and moisture obtained by multiple regression. This study further investigates the impacts of the new parameterization on the global carbon cycle budget. Our results show that non-uniform spatial distribution of Q10 tends to enhance heterogeneous anomaly of soil respiration comparing with the control simulation with uniform Q10. Moreover, it tends to improve the simulation of observed relationship between soil respiration and soil temperature and moisture, particularly over cold and dry regions. The new parameterization improves the simulation of gross primary production (GPP) by reducing bias in the global mean comparing with the FLUXNET-MTE observation data. Besides, GPP over high latitudes is significant increased by about two times from the control simulation. The realistic Rs and GPP simulation induced to represent carbon balance between release at the subsurface and uptake at the surface over terrestrial biosphere reasonably. Overall, enhanced heterogeneous temperature sensitivity in the soil decomposition process in the model showed the improvement of production and respiration. For evaluation of vegetation feedback on the climate, this study investigated the vegetation-climate feedback and impacts of vegetation change on the hydrological cycle in the East Asian monsoon region using comprehensive and developed UNIST-ESM. The intensity of East Asian summer monsoon (EASM) in the future increase due to enhance moisture flux at the surface by increased vegetation in EA. However, low-level relative humidity in the future decreases due to relatively increasing temperature comparing with enhanced moisture increase over EA. This process induces to suppress the formation of low-level cloud in the future. Therefore, enhanced incoming solar radiation over China regions is occurred by suppressed low-level cloud in the future climate. On the other hand, the exception of additional anthropogenic heating in future climate, the role of increase vegetation on the variation of EASM is opposite signal from the future climate scenarios. In terms of local hydrological process, the increased vegetation induces incareasing evapotranspiration and surface moisture flux over vegetated regions. This increment of moisture source from increased vegetated area tends to increase formation of low-level cloud due to small perturbation of temperature increase in this simulation. Enhanced amount of low-level cloud tends to decrease incoming solar radiation at the surface due to reflecting by clouds. It emphasized surface cooling in the increased vegetation regions. This surface cooling also affects to depress local vertical updraft over China where has large plants. Suppressed vertical updraft makes atmosphere stabilization over land area. The convective precipitation is affected to decrease by depressed vertical updraft associated with cooling temperature. In the focus of the large-scale circulation, the cooling temperature over vegetated area tends to decrease the land-sea contrast. Thermally more uniformed land and ocean surface make weak low-level circulation and meridional moisture transport over EA regions. This study suggested that the roles of vegetation to climate variation and hydrological cycle are homogenous not only location but also environmental climate conditions.

Development of a Second Harmonic Dual Mode Gyrotron for Generation of Orbital Angular Momentum Beam

Ashwini Sawant Graduate School of UNIST 2019 국내박사

This thesis presents the idea of the existence of the orbital angular momentum in gyrotron modes and includes the design process of a gyrotron source to demonstrate the generation of the OAM modes. The cavity modes of gyrotrons are rotating modes with no electrical field intensity along the axis. These modes are analogous to an energy packet revolving around an axis and generating an orbital angular momentum of order (l). We have numerically derived the existence of the orbital angular momentum in the gyrotron modes, which is proportional to the azimuthal index of the mode. We have reported the existence of the orbital angular momentum in gyrotron through a low power test carried out by a quasi-optical mode converter to generate a TE6,2 mode. We found out that the phase pattern of the emitted modes is having spiral patterns, which is the easiest way to identify the order of the low power OAM modes. We also presented a new modified phase-retrieval technique to determine the topological charges of the high-power OAM beams. The OAM property of the high-power gyrotron modes can be useful in wireless communication for enhancing the channel capacity and transmission distance. Development of a 190 GHz, dual mode gyrotron has been carried out for this work in UNIST. This gyrotron can operate on TE8,3 and TE11,2 mode to resonate at 188.5 GHz and 190.5 GHz respectively. The gyrotron is having an axial output, where the cavity modes are directly emitted into the free space through an overmoded tapered waveguide section to reduce its divergence. The gyrotron modes are second harmonic modes and generates around 30 kW of power with an efficiency of around 18%. To carry out the design simulations of the gyrotron, a time-dependent numerical code named as UNIST Gyrotron Design Tool (UGDT) has been developed. Second harmonic gyrotron modes are always susceptible to be suppressed by fundamental mode excitation. To avoid this fundamental mode excitation, the cavity opted for the gyrotron is a perturbed cavity with two sinusoidal perturbation at the straight section of the cavity to excite stable higher order axial modes. After a rigorous analysis of the perturbed cavity, a cavity with two sinusoidal perturbations and a raised cosine up-taper has been manufactured. Developed 190 GHz OAM gyrotron has been tested and its performance analysis has been carried out. The generated modes have been recognized based on the frequency measurements using heterodyne frequency measurement system. However, the preliminary results concluded in this thesis suggests the excitation of the desired TE8,3 mode have been observed along with the spurious fundamental mode excitation due to the alignment problem of the vacuum tube in the superconducting magnet. We confirmed this issue with the simulation results and will resolve it in our future work.

Evaluation of deposition sampler for polycyclic aromatic hydrocarbon monitoring

Kuen-Sik Jung Graduate School of UNIST 2014 국내석사

Polycyclic aromatic hydrocarbons (PAHs) are an important environmental concern due to their carcinogenic and toxic properties. Moreover, several PAHs have been classified into mutagenic compounds. The sources of PAHs are classified into anthropogenic and natural sources such as incomplete combustion of fossil fuel, biomass burning, industrial boilers, and forest fires etc. Emitted PAHs can distribute both gaseous phase and particulate phase. As a large amount of PAHs emitted to the atmosphere is deposited to the land or sea, atmospheric deposition of PAHs is a significant phenomenon. There have been many studies of atmospheric deposition of PAHs, and several kinds of deposition samplers have been used. However, the results with different deposition samplers cannot be directly compared, because their performance was not fully compared or calibrated. Besides, the deposition fluxes and deposition velocities measured in the previous studies showed large variations even though the same samplers were used. Therefore, a through evaluation of different types of deposition samplers are required to clearly understand the process of atmospheric deposition of PAHs. In this study, various information on widely used deposition samplers (basic theories, structures, and advantages/disadvantages) was collected. Then, the performance of four types of deposition samplers was evaluated. In addition, a high volume air sampler was used to investigate the ambient levels of PAHs and deposition velocities. The samplers were deployed on the roof of the engineering building #2 in the Ulsan National Institute of Science and Technology (UNIST) from May 2013 to October 2013. Four types of deposition samplers (dry deposition sampler (DDP), velcro deposition sampler, resin deposition sampler, and bulk deposition sampler) were used. Particulate and gaseous PAHs were indivisually collected by a high volume air sampler once a week. The target compounds in this study were thirteen US-EPA priority PAHs except naphthalene, acenaphthene, and acynaphthylene. After sample extraction and clean up using silica gel columns, a gas chromatograph/mass spectrometer (GC/MS) was used for PAH qualification and quantification. In order to further interpretate the source-recepor relationship of PAHs, houly data of criteria air pollutants (CO, SO2, NO2, O3, and PM10) measured nearby UNIST was acquired from the Ulsan Institute of Health and Environment (UIHE). The ranges of SO2 were 1.3–9.9 ppb (Mean: 3.8 ppb) and 3.4–15.0 ppb (Mean: 6.8 ppb) in Samnam and Mugeo air pollution monitoring stations. The SO2 level showed seasonal variations related with fossil fuel consumption and wind direction. The level of SO2 in Mugeo was higher than that of Samnam because Mugeo is more influenced by vehicles and has more urban characteristics. The ranges of NO2 were 6.7–21.9 ppb (Mean: 12.6 ppb) in Samnam and 4.7–43.1 ppb (Mean: 24.0 ppb) in Mugeo. The ranges of O3 were 14.1–63.9 ppb (Mean: 34.0 ppb) in Samnam and 13.5–60.5 ppb (Mean: 27.4 ppb) in Mugeo. The ranges of PM10 were 15.1–57.1 μg/m3 (Mean: 30.9 μg/m3) in Samnam and 14.6–74.8 μg/m3 (Mean: 38.4 μg/m3) in Mugeo. The sampling site at UNIST was confirmed to be seasonally influenced by air pollution sources in Samnam and Mugeo according to geographical positions and major wind directions. The levels of gaseous PAHs were 1.10–7.02 ng/m3 (Mean: 4.23 ng/m3), and those of particulate PAHs were 0.85–2.82 ng/m3 (Mean: 1.67 ng/m3). Namely, the total PAH concentrations were 1.95–9.84 ng/m3 (Mean: 5.91 ng/m3) during the sampling period. The variation of PAH concentrations was not large, but they increased in spring and fall. The sampling site in this study is located in a rural area. Therefore, it was assumed that the sampling site was affected by criteria air pollutants and PAHs emitted from urban sources. Deposition fluxes and velocities of PAHs were calculated based on the amount of deposited PAHs and ambient air concentrations. The ranges of deposition fluxes of PAHs collected by DDP, velcro, resin, and bulk samplers were 4.55–15.13 μg/m2/d (Mean: 8.89 μg/m2/d), 13.14–30.92 μg/m2/d (Mean: 22.04 μg/m2/d), 7.72–55.41 μg/m2/d (Mean: 28.43 μg/m2/d), and 32.72–49.44 μg/m2/d (Mean: 40.13 μg/m2/d), respectively. This result indicates that deposition fluxes derived from different types of deposition samplers do not coincide and they should not be directly compared. DDP could not collect high molecular weight-PAHs mostly associated with fine particles. Therefore, the performance of the velcro sampler as a dry deposition sampler was better than that of DDP. As a bulk (dry/wet deposition) sampler, the performance of the Resin and bulk samplers was similar. On the basis of this result, further studies were suggested to improve the calculation of deposition fluxes and velocities.

Evaluation of deposition samplers for polycyclic aromatic hydrocarbon monitoring

정근식 Graduate School of UNIST 2014 국내석사

Polycyclic aromatic hydrocarbons (PAHs) are an important environmental concern due to their carcinogenic and toxic properties. Moreover, several PAHs have been classified into mutagenic compounds. The sources of PAHs are classified into anthropogenic and natural sources such as incomplete combustion of fossil fuel, biomass burning, industrial boilers, and forest fires etc. Emitted PAHs can distribute both gaseous phase and particulate phase. As a large amount of PAHs emitted to the atmosphere is deposited to the land or sea, atmospheric deposition of PAHs is a significant phenomenon. There have been many studies of atmospheric deposition of PAHs, and several kinds of deposition samplers have been used. However, the results with different deposition samplers cannot be directly compared, because their performance was not fully compared or calibrated. Besides, the deposition fluxes and deposition velocities measured in the previous studies showed large variations even though the same samplers were used. Therefore, a through evaluation of different types of deposition samplers are required to clearly understand the process of atmospheric deposition of PAHs. In this study, various information on widely used deposition samplers (basic theories, structures, and advantages/disadvantages) was collected. Then, the performance of four types of deposition samplers was evaluated. In addition, a high volume air sampler was used to investigate the ambient levels of PAHs and deposition velocities. The samplers were deployed on the roof of the engineering building #2 in the Ulsan National Institute of Science and Technology (UNIST) from May 2013 to October 2013. Four types of deposition samplers (dry deposition sampler (DDP), velcro deposition sampler, resin deposition sampler, and bulk deposition sampler) were used. Particulate and gaseous PAHs were indivisually collected by a high volume air sampler once a week. The target compounds in this study were thirteen US-EPA priority PAHs except naphthalene, acenaphthene, and acynaphthylene. After sample extraction and clean up using silica gel columns, a gas chromatograph/mass spectrometer (GC/MS) was used for PAH qualification and quantification. In order to further interpretate the source-recepor relationship of PAHs, houly data of criteria air pollutants (CO, SO2, NO2, O3, and PM10) measured nearby UNIST was acquired from the Ulsan Institute of Health and Environment (UIHE). The ranges of SO2 were 1.3–9.9 ppb (Mean: 3.8 ppb) and 3.4–15.0 ppb (Mean: 6.8 ppb) in Samnam and Mugeo air pollution monitoring stations. The SO2 level showed seasonal variations related with fossil fuel consumption and wind direction. The level of SO2 in Mugeo was higher than that of Samnam because Mugeo is more influenced by vehicles and has more urban characteristics. The ranges of NO2 were 6.7–21.9 ppb (Mean: 12.6 ppb) in Samnam and 4.7–43.1 ppb (Mean: 24.0 ppb) in Mugeo. The ranges of O3 were 14.1–63.9 ppb (Mean: 34.0 ppb) in Samnam and 13.5–60.5 ppb (Mean: 27.4 ppb) in Mugeo. The ranges of PM10 were 15.1–57.1 μg/m3 (Mean: 30.9 μg/m3) in Samnam and 14.6–74.8 μg/m3 (Mean: 38.4 μg/m3) in Mugeo. The sampling site at UNIST was confirmed to be seasonally influenced by air pollution sources in Samnam and Mugeo according to geographical positions and major wind directions. The levels of gaseous PAHs were 1.10–7.02 ng/m3 (Mean: 4.23 ng/m3), and those of particulate PAHs were 0.85–2.82 ng/m3 (Mean: 1.67 ng/m3). Namely, the total PAH concentrations were 1.95–9.84 ng/m3 (Mean: 5.91 ng/m3) during the sampling period. The variation of PAH concentrations was not large, but they increased in spring and fall. The sampling site in this study is located in a rural area. Therefore, it was assumed that the sampling site was affected by criteria air pollutants and PAHs emitted from urban sources. Deposition fluxes and velocities of PAHs were calculated based on the amount of deposited PAHs and ambient air concentrations. The ranges of deposition fluxes of PAHs collected by DDP, velcro, resin, and bulk samplers were 4.55–15.13 μg/m2/d (Mean: 8.89 μg/m2/d), 13.14–30.92 μg/m2/d (Mean: 22.04 μg/m2/d), 7.72–55.41 μg/m2/d (Mean: 28.43 μg/m2/d), and 32.72–49.44 μg/m2/d (Mean: 40.13 μg/m2/d), respectively. This result indicates that deposition fluxes derived from different types of deposition samplers do not coincide and they should not be directly compared. DDP could not collect high molecular weight-PAHs mostly associated with fine particles. Therefore, the performance of the velcro sampler as a dry deposition sampler was better than that of DDP. As a bulk (dry/wet deposition) sampler, the performance of the Resin and bulk samplers was similar. On the basis of this result, further studies were suggested to improve the calculation of deposition fluxes and velocities.

Generation of Windowed Multipole Library for on-the-fly Doppler Broadening in UNIST In-house Monte Carlo Code

Azamat Khassenov Graduate School of UNIST 2018 국내석사

This thesis presents the generation and application results of the windowed multipole (WMP) library in UNIST in-house Monte Carlo code (MCS). The given library is used in the on-the-fly Doppler broadening of microscopic cross section at the temperature of the interest during a Monte Carlo simulation. This feature is one of the major requirements for multi-physics simulations; in other words, coupled calculations of neutron transport, thermal-hydraulics, and fuel performance codes. A windowed multipole library significantly reduces the memory necessary for cross section storage with a reasonable increase in the total Monte Carlo simulation time. The ENDF/B-VII.1 neutron induced library contains information on 430 isotopes, where 331 contain resonance parameters for the resolved resonance region. In the first step, the parameters from the evaluated nuclear data file were converted into corresponding rigorous multipole parameters, which can be directly used in temperature dependent cross section reconstruction. Further, in order to reduce the cross section generation time the energy window concept was applied with an accuracy threshold of 0.1 % relative difference in comparison to the reference cross section. The accuracy and effect of the generated windowed multipole library on the MCS simulation was evaluated using fresh and burned PWR fuel pins, and assemblies.

III-N LEDs with graphene double-sided InGaN/GaN multiple quantum well structures

Goh-Myeong Bae Graduate school of UNIST 2015 국내석사

For a decade, graphene has been mainly used for III-nitrides based light emitting diodes (LEDs) as a transparent and current spreading layer by chemical vapor deposition (CVD) growth method. Herein, we report new stack design, graphene double-sided InGaN/GaN multiple quantum well structures, which can be applied as both a buffer layer and a transparent conducting electrode. The InGaN/GaN MQW structures on graphene buffered GaN template show enhancement of indium phase separation with a rougher GaN surface than conventional MQW systems on two-step growth GaN films. The MQW structures on one-step GaN using graphene coating layer display high internal quantum efficiency (IQE) value and negligible emission wavelength peak shift along current density change, which is similar characterization of polarization free quantum dots (QDs). Furthermore, a CVD monolayer graphene transferred onto the top of the p-GaN/MQWs/n-GaN/u-GaN/graphene/sapphire heterosystem, which has high transmittance in ultraviolet regions than indium tin oxide (ITO) layer and lower forward voltage than MQW structures with sole graphene buffer layer. This unique stacking method diversifies graphene applications for future optoelectronic devices based on III-Ns compound semiconductor.

Mono-layered Photonic Crystal Patterning for Anti-counterfeit Applications of Structural Colors

Hyunmoon Nam Graduate school of UNIST 2015 국내석사

Photonic crystals (PCs) can manipulate electromagnetic wave by designing artificial periodic dielectrics, which provides various applications such as sensor, LED, laser, and optical computers. Recently, many studies focus on display applications by designing photonic band-gap while the fabrication of photonic crystals in a nanoscale is still challenging. In this work, a simple method is described for fabricating mono-layered self-assembled photonic crystals (SAPCs) by using inkjet material printers that are able to inject nanoparticle suspension on a substrate in contrast to conventional approaches such as photo-lithography, two-photon patterning, and direct-write assembly. For making homogeneous single-layered structure, crucial factors influencing the micro-patterns of a colloidal assembly of the inkjet-printed droplet were investigated including the substrate wettability and chemical composition of ink to see what effect they might have on producing structure color. These patterned photonic crystals yield stealth ability to avoid pattern detection from counterfeiters under day light illumination and generate multiple colorful holograms on different viewing angles for complex cryptography. In addition, the number of SAPCs in a matrix format controls optical intensities, thus yielding extra anti-counterfeiting function. Because the inkjet-printed-based SAPC platforms provides a simple and the unique optical properties, it is believed that the approach can be widely used for anti-counterfeiting systems.

Structure-Property Relationship Studies for High-Performance Organic Field-Effect Transistors and Flexible Photosensors

Jayeon Hong Graduate school of UNIST 2015 국내석사

Recently, organic field-effect transistors (OFETs) and OFET-based sensors have attracted great interest for their potential for use in low-cost, large-area, lightweight, flexible, and wearable electronic devices. Various researches for high-performance OFET devices have been reported to achieve high mobility, air stability, and flexibility through molecular design and optimized device configuration. In addition, OFET-based sensors based on various flexible substrates and nanostructured organic semiconducting materials have been studied for use in wearable sensor devices with high sensitivity and excellent mechanical stability under severely bent condition. In chapter 1, we studied the relationship between molecular structure in a film state and electrical performance of OFET devices. We fabricated high-performance n-channel OFETs based on semiconducting copolymers containing strong electron-withdrawing unit, naphthalene diimide (NDI). NDI-based copolymers with various donor moieties, acene- (benzene (Bz), naphthalene (Np), and pyrene (Py)) and heteroacene-type components (selenophene (Se) and thiophene (Th)) were designed to enhance efficient intramolecular charge transfer (ICT). The OFET performance of NDI-based copolymers was optimized in bottom-gate top-contact (BGTC) device configuration by tuning the solution-deposition methods and thermal annealing at various temperatures. The electrical characteristics of the devices fabricated with PNDI-Np, acene-based centrosymmetric copolymer, showed the best electron mobility of 5.63×10-2 cm2V-1s-1 among the developed polymers including axisymmetric copolymers with electron-rich donor groups. This result reveals the stronger influence of the geometric feature on the OFET performance rather than electron-donating strength of the donors in the molecular backbone. In chapter 2, we report on highly flexible OFET-based photosensors based on a textile substrate and organic semiconducting nanofibers. Textile-based OFET devices with bottom-gate bottom-contact (BGBC) configuration consist of poly(ethylene terephthalate) (PET) textile substrate buffered with polydimethylsiloxane (PDMS), gate electrode, PDMS dielectric layer and source-drain electrode. Electrospun organic semiconducting nanofibers based on a p-type semiconducting polymer, poly(3,3‴-didodecylquarterthiophene) (PQT-12) were used as the active layer. The field-effect mobility of textile-based OFETs was as high as 2.96×10-3 cm2V-1s-1 in N2 atmosphere. Under the bending test with extremely low bending radius of 0.75 mm, the device performance showed superior mechanical stability compared with the PET film-type substrates or PDMS-only substrates. Furthermore, they exhibited highly stable electrical characteristics after ~1000 cycles of bending test. The electrical responses of textile-based OFETs with photo-responsive organic semiconducting nanofibers were also investigated under the irradiation of light with various wavelengths. The developed method may pave a viable way for the fabrication of wearable photosensing or photoswitching devices.

Polymeric Nanogel for Non-covalent Hydrophobic Drug Encapsulation

Boram Bae Graduate school of UNIST 2015 국내석사

Nanomedicine, the nanotechnology for development of efficient and safe medicines affects to biotechnology and chemistry during several decades.The interest in nanomedicine offers the innovation of drug delivery system using nanoparticle. The advantages of nanoparticles in the therapeutic application includes following properties. First, they can enhance the effect of medicines without displace other drug molecules for pharmacokinetic effects. Second, the specificity to the diseased cell by targeting delivery showed efficiency than chemotherapy. Third, they can across the primary barrier to the immunological response. Nowadays, the modifiable drug carrier performs multimodal delivery with the imaging agent and therapeutic reagent. They can pack diverse cargo molecules such as proteins, peptides, genes, sugar as well as a variety of chemical reagents. Especially, the targeting ability of nanoparticle system has attractive property to development. Passive targeting is one kind of focusing mechanism of nanoparticle. The nanoparticle can be accumulated in the active site in targeting site with cell population. Active targeting is the other way for targeting method of nanoparticle. The key to this method is surface modification. Conjugation with affinity ligands provides the unique binding ability with disease tissues and cells. Through past 30 years, there were quite a number of nanoparticle models developed for the therapeutic purpose. However, only a very few of nanoparticles applied in clinical development and none of them have been used for clinical purpose. The lack of understanding phenomenon inside cellular level with nanoparticle and reproduction problem for synthesis nanoparticle hampers the clinical translation. In this thesis, we treated several researches trying to solve current problems in drug delivery area. First, the study of investigating of cargo release mechanism using polymeric micelles would give us the useful solution for developing future theragnostic nanoparticle. We used well-known polymeric micelle system which includes biocompatibility and resistance to cytotoxicity. Clear understanding of a cellular pathway for release drug molecules will open the gate for clinical application. Second, we developed the natural polypeptide based supramolecular nanogels for resolve current premature release problems. The biocompatible nanoparticle including the ability regarding triggered release will give us the other possibility using natural polypeptide as the material for nanogel system. Lastly, the nanoparticle models with unique targeting ability are developed following the current trend of this research area. Their particular advantage for affinity and targeting subcellular organelles provides more efficient way for cure disease through nanoparticle systems.