Rheological and Physical Properties of Sulfonated Polystyrene Ionomer Solutions and the Membranes

채동욱,최경락,김병철,Chae, Dong Wook,Choi, Kyung Rak,Kim, Byoung Chul The Korean Fiber Society 2018 한국섬유공학회지 Vol.55 No.1

The rheological properties of sulfonated polystyrene (SPS) ionomer solutions were found to be significantly affected by solvent polarity, counterion, sulfonation level, and temperature. In the dilute concentration regime, the reduced viscosity (${\eta}_{red}$) of SPS solutions in the dimethyl sulfoxide (DMSO), which is a polar solvent, increased with decreasing concentration, whereas opposite effects were observed in low-polarity solvent tetrahydrofuran (THF). H-SPS solutions in THF showed typical shear-thinning behavior over all the measured frequencies, while solutions in DMSO showed shear-thickening behavior at low shear rates, followed by shear-thinning behavior at higher shear rates. These different behaviors might result from differences in polymer-solvent interactions and the chain conformation. SPS solutions in DMSO containing monovalent ions ($Na^+$) exhibited higher dynamic viscosity values than those with divalent ions ($Ca^{2+}$, $Mg^{2+}$) because of the different degrees of chain expansion. In DMSO, the dynamic viscosity increased with temperature, regardless of the sulfonation level and counterion. Both the proton conductivity and methanol permeability of the SPS membranes increased with increasing sulfonation level and exhibited an abrupt increase between 10 and 15 mol%, indicative of a percolation threshold.

Effects of Swelling Conditions on the Superstructure of PVA Films during the Wet Drawing Process

채동욱,김영우,이은정,김병철,Chae, Dong Wook,Kim, Young Woo,Lee, Eun Jeoung,Kim, Byoung Chul The Korean Fiber Society 2016 한국섬유공학회지 Vol.53 No.3

The effects of swelling conditions on the superstructure of polyvinyl alcohol (PVA) films containing 10 wt% glycerol were investigated. The water content of PVA films increased as the swelling temperature and swelling time increased. An abrupt increase in water content was observed between 40 and $50^{\circ}C$ in the vicinity of $T_g$ of PVA. The water content leveled off after approximately 100 s at all swelling temperatures except $50^{\circ}C$, where it decreased after approximately 200 s. In the differential scanning calorimeter (DSC) measurement, the peak temperature for water evaporation was shifted to a value higher than $100^{\circ}C$ and became sharper with increasing swelling temperature. Wide angle X-ray diffraction (WAXD) profiles of PVA films revealed that the degree of crystallization had decreased with increasing water content; however, the average crystal size remained largely unchanged. For PVA films drawn at $50^{\circ}C$ in water, the diffraction peak for the (101) plane became sharper and increased with draw ratio. The degree of crystallization of swollen PVA films in water significantly increased with increasing draw ratio, whereas there was no noticeable change in the crystal size.

Structural Characterization and Physical Properties of Poly(ethylene terephthalate) and Poly(trimethylene terephthalate) Blends: Effects of Blending Time and Blend Ratio

채동욱,최경락,김병철,Chae, Dong Wook,Choi, Kyung Rak,Kim, Byoung Chul The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.3

Poly(ethylene terephthalate) (PET) and poly(trimethylene terephthalate) (PTT) were melt blended at $280^{\circ}C$ at varying blending time and ratio. The resulting physical properties were examined in relation to ester exchange reactions. The PET/PTT 50/50 blends (by weight percentage) exhibited double melting peaks ($T_m$) up to 30 min blending time beyond which they were merged to one broader peak. The melting peak had a nearly linear relationship with blending time and displayed a much steeper decrease for ET units than for TT units. Two new peaks for asymmetric aromatic carbons were detected in $^{13}C$-NMR spectra and their intensity increased notably from 40 min blending time which was consistent with thermal analysis. The dissolution of copolyesters occurred even after 10 min blending time and its degree increased with blending time. FESEM images of chloroform etched fracture surfaces displayed coarse and continuous phase properties from 40 min blending time while losing the spherical shape of each component. In the DSC measurement of the PET/PTT blends prepared at various ratios at a given blending time of 20 min, all the blends exhibited a single glass transition temperature ($T_g$) more consistent with the Gordon-Taylor equation than the Fox equation. In addition, a single $T_m$ peak was observed in each sample, except for 50/50 composition, which shows the coexistence of $T_m$ for each component. All blends except for 50/50 exhibited a similar WAXD patterns to their rich component. This was evidenced by solubility test results showing the highest solubility for 50/50 blends. This phenomenon was also confirmed in FESEM measurement of chloroform etched fracture surfaces where the blends composed of an equal amount of the component exhibited coarse and dumbbell-like domains.

Rheological Properties of PAN/DMF Spinning Solutions and Physical Properties of Conducting Carbon Nanofibers Prepared by Electrospinning and Carbonization

채동욱,권오주,이은정,김병철,Chae, Dong Wook,Kwon, Oh Joo,Lee, Eun Jeoung,Kim, Byoung Chul The Korean Fiber Society 2016 한국섬유공학회지 Vol.53 No.5

Dynamic rheological properties of polyacrylonitrile (PAN)/dimethylformamide (DMF) solutions were measured at several different temperatures ($25-55^{\circ}C$), and their electrospinning was conducted at corresponding temperatures to prepare PAN precursor fibers. The electrospun fibers were subsequently converted to carbon nanofibers through a carbonization process and their physical properties such as electrical conductivity, morphology and crystal structure were examined with regard to the electrospinning temperature. The dynamic viscosity of PAN/DMF solutions decreased with increasing temperature, exhibiting a lower Newtonian flow region followed by shear thinning. In the Cole-Cole plot, the initial slope decreased with decreasing temperature but a single master curve of constant slope above the inflection point was observed regardless of the temperature. FESEM images showed that the diameter of the PAN precursor fibers and resulting carbon nanofibers decreased as the electrospinning temperature increased. The diffraction peak of carbon nanofiber in the WAXD pattern was shifted from 22 to $24^{\circ}$. Further, Raman spectroscopy showed that the graphitic carbon peak at $1600cm^{-1}$ increased with increasing electrospinning temperature. In addition, the electrical conductivity of the carbon nanofiber increased considerably from 2.95 to 6.15 S/cm with increasing electrospinning temperature from 25 to $55^{\circ}C$.

Effects of Stress Level and Temperature on the Time Dependent Morphological and Physical Properties of PVA Fibers

채동욱,김승규,김병철,Chae, Dong Wook,Kim, Seung Gyoo,Kim, Byoung Chul The Korean Fiber Society 2017 한국섬유공학회지 Vol.54 No.2

The effects of the stress level and heat treatment temperature on the morphological and physical properties of poly(vinyl alcohol) (PVA) fibers were investigated with regard to treatment time. The PVA fibers were heat treated at three different temperatures (210, 220, and $230^{\circ}C$) and stress levels (0.05, 0.15, and 0.25 g/d). Increase in shrinkage was observed with an increase in the heat treatment time when treated at 220 and $230^{\circ}C$ beyond 15 min, while a little extension was observed at $210^{\circ}C$. The shrinkage in the PVA fibers heat treated at $230^{\circ}C$ increased with a decrease in stress levels, exhibiting a different dependence of the shrinkage on the heat treatment time. The WAXS patterns of the PVA fibers heat treated at $230^{\circ}C$ at 0.15 g/d showed that the crystalline peaks became sharp with time up to 15 min beyond which they became dull. The degree of crystallinity, determined from the density measurement, was maximum when heat treated for 5 min regardless of the temperature and the stress level. However, the degree of crystallinity when further treated at 220 and $230^{\circ}C$ decreased, while that showed little change when treated at $210^{\circ}C$. In addition, the variation of the degree of crystallinity with heat treatment time was in good agreement with that of the degree of amorphous orientation. In the DSC thermograms, a greater dependence of the melting temperature and the heat of fusion on the heat treatment time was observed at higher heat treatment temperatures and lower stress levels.

A Novel Approach to Disentangle Carbon Nanotubes Using Viscous Sugar Syrup

Dong Wook Chae(채동욱),Stephen C. Hawkins,Chi P. Huynh,Youngho Eom(엄영호),Youkyung Han(한유경),Bong-Seob Shin(신봉섭),Jong-Young Jeon(전종영) 한국고분자학회 2020 폴리머 Vol.44 No.4

끈적끈적한 설탕시럽을 사용한 다중벽 탄소나노튜브(MWNT) 번들의 풀림이 연구되었다. 시럽은 수크로스, 글루코스, 프럭토스와 증류수를 1:1:1:0.8의 무게 비율로 혼합하여 제조되었다. 고점도의 물질을 위한 디스크형태의 믹서가 시럽과 MWNTs를 혼합하기 위하여 제작되었다. MWNT의 효과적인 풀림을 위한 최적의 혼합조건을 알기 위하여 MWNT/설탕시럽 함량 비율을 각 제조단계에서 다양하게 하였다. 설탕시럽에서 나노튜브의 분산상태를 정량적으로 평가하기 위해 디지털영상처리기술이 광학현미경 이미지에 사용되었다. 이것은 MWNT의 균일한 분산이 시럽을 한 번에 첨가하기보다는 각 단계에서 점차적으로 첨가함으로써 얻어진다는 것을 보여주었다. 혼합물의 동적점도가 MWNT의 전체적인 분산상태를 평가하기 위해서 측정되었다. MWNT 첨가가 시럽의 동적점도를 증가시켰고 분산정도가 증가하면서 동적점도가 감소함을 보였다. 이 새로운 분산방법을 고분자 복합체에 적용가능한지 입증하기 위해서 분산된 MWNT가 폴리비닐알콜과 폴리아크릴로니트릴에 옮겨졌고 각 매트릭스에서 재뭉침없이 균일하게 분산됨을 보였다. The disentanglement of multi-walled carbon nanotube (MWNT) bundles by using a sticky sugar syrup was explored for the first time. The syrup was prepared by mixing sucrose, glucose, fructose, and distilled water in a 1:1:1:0.8 weight ratio. A disk-type mixer suitable for high-viscosity materials was built to mix this syrup with MWNTs. To find out the optimum mixing conditions for effective disentanglement of MWNTs, the content ratio of MWNTs to sugar syrup was varied at each mixing step. Digital image processing technique was used with optical micrographs to quantitatively estimate the dispersion of nanotubes in sugar syrups. This revealed that the most homogeneous dispersion of MWNTs in the sugar syrup was achieved by gradually adding the syrup at each mixing step rather than all at once at the initial mixing step. The dynamic viscosity (η") of the mixtures was measured to evaluate the overall dispersion state of MWNTs. The incorporation of MWNTs increased the η" of sugar syrup, exhibiting a decreased η" with an increase in the degree of dispersion. To validate this novel dispersion method for polymer composites, disentangled MWNTs were transferred into poly(vinyl alcohol) (PVA) and polyacrylonitrile (PAN); they exhibited uniform dispersion in each polymer matrix, without reagglomeration occurred.

Rheological Characterization of the Gelation Behavior of PVA Solutions in DMSO Containing BA

이은정,김동준,채동욱,김병철,Lee, Eun Jeoung,Kim, Dong Jun,Chae, Dong Wook,Kim, Byoung Chul The Korean Fiber Society 2018 한국섬유공학회지 Vol.55 No.3

The gelation behavior of poly(vinyl alcohol) (PVA) solutions in dimethyl sulfoxide (DMSO) containing boric acid (BA, $H_3BO_3$) under shear stress was rheologically investigated in terms of temperature and molecular weight of PVA. Time-dependent rheological properties of the solutions were analyzed to determine the effects of stress on the gelation mechanism. The solutions of low weight-average molecular weight ($M_w=31,000-50,000$) PVA showed more noticeable temperature-dependent viscosity changes than those of high weight-average molecular weight ($M_w=165,000-186,000$) PVA. The viscosity increase caused by stress indicated that the formation of the gel structure was promoted by stress. In time sweep experiments, all the PVA solutions showed stress-dependent rheological responses except for the high $M_w$ PVA solutions at $30^{\circ}C$. The viscosities of the solutions remained constant over the observed shearing time, indicating the formation of an irreversible gel. The effects of stress history were reconfirmed by the results of frequency sweep experiments. Antecedent shearing gave rise to many different time-dependent rheological responses. At $60^{\circ}C$, both low and high $M_w$ PVA solutions had loss tangent values (tan ${\delta}$) less than 1. Furthermore, the formation of gel structures increased the relaxation time (${\lambda}$) by up to 10 s.

Effects of Annealing Conditions on the Physical Properties of Poly(1-oxotrimethylene) Fibers

배원식,최수명,김병철,채동욱,Bae, Won-Sik,Choi, Soo-Myung,Kim, Byoung-Chul,Chae, Dong-Wook The Korean Fiber Society 2011 한국섬유공학회지 Vol.48 No.6

The effects of annealing on the physical properties of poly(1-oxotrimethylene) (POTM) fibers were investigated in terms of draw ratio (DR). Annealing increased the degree of orientation with increasing DR. Analysis of wide angle X-ray diffraction patterns and Raman spectra suggested that annealing caused crystal structure transition from the ${\beta}$-form to the ${\alpha}$-form, which had a denser and more perfect crystal structure. The ${\beta}$-form and ${\alpha}$-form crystals were favorably formed for as-spun fibers and DR 13 fibers, respectively. In the fiber of DR 4, a combination of both ${\alpha}$- and ${\beta}$-form crystals was observed. Once the fiber was melted, no melt crystallization took place during cooling. Infrared spectra revealed that the melting process changed the chemical composition of POTM fibers by thermal decomposition, resulting in disappearance of the melt crystallization. In the stress-strain (SS) curve, the as-spun fibers exhibited yield behavior and a plateau region, while the drawn fibers gave a typical SS curve of brittle material without a plateau region. POTM fibers of DR 13 exhibited a significant increase in tensile modulus compared with as-spun and DR 4 fibers.

Controlling Internal Pore Structure of Porous Carbon Nanofibers Based on the Miscibility between Polyacrylonitrile Matrix and Sacrificial Polymers

Hyunmin Hwang(황현민),Dong Wook Chae(채동욱),Youngho Eom(엄영호) 한국고분자학회 2021 폴리머 Vol.45 No.2

폴리아크릴로니트릴(PAN) 기반 혼합 용액의 전기방사를 통해 다공성 탄소나노섬유를 제조하였으며, 혼합된 고분자와 PAN 간 혼화성이 기공 구조에 미치는 영향이 연구되었다. 탄화 후 다공성을 부여하기 위해 희생용 고분자로 폴리비닐리덴플로우라이드(PVDF)와 스티렌-아크릴로니트릴 공중합체(SAN) 두 종이 선택되었고, PAN과 두 희생용 고분자 간 혼화성은 이론 및 실험적으로 평가되었다. 용해도 지수 분석 결과 SAN보다 PVDF가 쌍극자-쌍극자 상호작용을 통해 PAN과 더 가까운 친화성을 가짐이 증명되었다. PAN과 SAN(1.19)보다 PVDF(0.52) 간 더 낮은 용해도 지수 값은 PAN-PVDF계의 더 우수한 혼화성을 정량적으로 뒷받침해주었다. PAN/PVDF 혼합 필름의 동적 기계 분석에서, PAN과 PVDF의 유리전이온도를 나타내는 손실 탄젠트(tan δ) 피크가 각각 관찰되었고 서로를 향하여 이동하는 현상은 두 고분자의 부분적 혼화성을 입증하였다. 하지만, PAN/SAN 혼합필름의 경우, PAN의 tan δ피크 이동이 미미하였고, 이는 낮은 혼화성을 나타내는 이론적 분석 결과와 일치하였다. 탄화 후 PVDF계 혼합섬유는 길쭉한 형태의 기공구조를 보이는 반면, SAN계는 원형 기공구조를 가졌다. 이러한 기공구조의 차이는 두 희생용 고분자와 PAN 간의 혼화성 차이에 기인하였다. Porous carbon nanofibers were prepared via electrospinning of polyacrylonitrile (PAN)-based blend solutions and effects of miscibility of the blended polymers on pore structure were investigated. Two sacrificial polymers, poly(vinylidene fluoride) (PVDF) and poly(styrene-co-acrylonitrile) (SAN), were chosen as a sacrificial component to yield porosity after carbonization. The miscibility of PAN with each sacrificial polymer was evaluated both theoretically and empirically. Analyzing solubility parameters revealed that PVDF had higher chemical affinity with PAN due to dipole-dipole interaction than SAN. Lower value of Flory-Huggins interaction parameter of PAN with PVDF (0.52) than with SAN (1.19) quantitatively confirmed the better miscibility of PAN-PVDF. In dynamic mechanical analysis of PAN/PVDF blend films, individual loss tangent (tan δ) peaks (i.e., glass transition peak) for PAN and PVDF were observed but they were shifted to each other, indicating partial miscibility. In PAN/SAN films, however, the peak shift of PAN was negligible. These results coincided well with the theoretical analysis. After carbonization, the blend nanofibers exhibited high porosity with different pore structures; elongated shape for PVDF and round shape for SAN system. The pore structure discrepancy in the two systems was ascribed to the miscibility difference of each sacrificial polymer with PAN matrix.

능동 지능형 현가장치의 제어로직 신뢰성 실차 평가

윤득선(Duk Sun Yun),채동욱(Dong Wook Chae),강호준(Ho Joon Kang),송세일(Se Il Song) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5

The active geometry control suspension, which is designed by HyundaiㆍKia Motor Company, is unique system. This system has installed at Sonata 2.4 model and it evaluated on vehicle performance before. This paper deals the reliability evaluation for the suspension system, therefore, it should contains wide range of test categories. However, authors focus on the proving ground test with single lane change, double lane change, and slalom passing histories. In addition, the results on the proving ground compare with the results of without active geometry control suspension system for the control logic reliability.