• Title/Summary/Keyword: Proton diffusion coefficient

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On the Chemical Diffusion Coefficient of H2O in AB1-xBxO(3-x/2)-type Perobskites

  • Baek, Hyun-Deok;Virkar, Anil V.
    • Journal of the Korean Ceramic Society
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    • v.40 no.9
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    • pp.827-831
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    • 2003
  • In proton-conducting perovskites, oxygen ions and protons make a diffusion pair for a chemical diffusion and thus lead to the transport of $H_2O$ under its chemical potential gradient. The present manuscript develops relationships between the chemical diffusion coefficient of $H_2O$ and the diffusion coefficients of protons and oxygen vacancies with an emphasis on the thermodynamic behavior of the oxygen vacancies. Depending on the degree of hydration X, two different expressions of the chemical diffusion coefficient were obtained : equation omitted and equation omitted.

Transport of Water through Polymer Membrane in Proton Exchange Membrane Fuel Cells (고분자전해질 연료전지에서 고분자막을 통한 물의 이동)

  • Lee, Daewoong;Hwang, Byungchan;Lim, Daehyun;Chung, Hoi-Bum;You, Seung-Eul;Ku, Young-Mo;Park, Kwonpil
    • Korean Chemical Engineering Research
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    • v.57 no.3
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    • pp.338-343
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    • 2019
  • The water transport and water content of the electrolyte membrane greatly affect the performance of the membrane in PEMFC(Proton Exchange Membrane Fuel Cell). In this study, the parameters (electroosmotic coefficient, water diffusion coefficient) of polymer membranes for water transport were measured by a simple method, and water flux and ion conductivity were simulated by using a model equation. One dimensional steady state model equation was constructed by using only the electro-osmosis and diffusion as the driving force of water transport. The governing equations were simulated with MATLAB. The electro-osmotic coefficient of $144{\mu}m$ thick polymer membranes was measured in hydrogen pumping cell, the value was 1.11. The water diffusion coefficient was expressed as a function of relative humidity and the activation energy for water diffusion was $2,889kJ/mol{\cdot}K$. The water flux and ion conductivity results simulated by applying these coefficients showed good agreement with the experimental data.

Synthesis and Characterization of Sulfonated Poly(arylene ether) Polyimide Multiblock Copolymers for Proton Exchange Membranes

  • Lee, Hae-Seung;Roy Abhishek;Badami Anand S.;McGrath James E.
    • Macromolecular Research
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    • v.15 no.2
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    • pp.160-166
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    • 2007
  • Novel multiblock copolymers, based on segmented sulfonated hydrophilic-hydrophobic blocks, were synthesized and investigated for their application as proton exchange membranes. A series of segmented sulfonated poly(arylene ether sulfone)-b-polyimide multiblock copolymers, with various block lengths, were synthesized via the coupling reaction between the terminal amine moieties on the hydrophilic blocks and naphthalene anhydride functionalized hydrophobic blocks. Successful imidization reactions required a mixed solvent system, comprised of NMP and m-cresol, in the presence of catalysts. Proton conductivity measurements revealed that the proton conductivity improved with increasing hydrophilic and hydrophobic block lengths. The morphological structure of the multiblock copolymers was investigated using tapping mode atomic force microscopy (TM-AFM). The AFM images of the copolymers demonstrated well-defined nanophase separated morphologies, with the changes in the block length having a pronounced effect on the phase separated morphologies of the system. The self diffusion coefficient of water, as measured by $^1H$ NMR, provided a better understanding of the transport process. Thus, the block copolymers showed higher values than Nafion, and comparable proton conductivities in liquid water, as well as under partially hydrated conditions at $80^{\circ}C$. The new materials are strong candidates for use in PEM systems.

A Review of Brain Magnetic Resonance Imaging Correlates of Successful Cognitive Aging (뇌자기공명영상의 노화에 따른 변화)

  • Ji, Eun-Kyung;Chung, In-Won;Youn, Tak
    • Korean Journal of Biological Psychiatry
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    • v.21 no.1
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    • pp.1-13
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    • 2014
  • Normal aging causes changes in the brain volume, connection, function and cognition. The brain changes with increases in age and difference of gender varies at all levels. Studies about normal brain aging using various brain magnetic resonance imaging (MRI) variables such as gray and white matter structural imaging, proton spectroscopy, apparent diffusion coefficient, diffusion tensor imaging and functional MRI are reviewed. Total volume of brain increases after birth but decreases after 9 years old. During adulthood, total volume of brain is relatively stable. After 35 years old, brain shrinks gradually. The changes of gray and white matters by aging show different features. N-acetylaspartate decreases or remains unchanged but choline, creatine and myo-inositol increase with aging. Apparent diffusion coefficient decreases till 20 years old and then becomes stable during adulthood and increase after 60 years old. Diffusion tensor properties in white matter tissue are variable during aging. Resting-state functional connectivity decreases after middle age. Structural and functional brain changes with normal aging are important for studying various psychiatric diseases such as dementia, schizophrenia and bipolar disorder. Our review may be helpful for studying longitudinal changes of these diseases and successful aging.

Ex Vivo MR Diffusion Coefficient Measurement of Human Gastric Tissue (인체의 위 조직 시료에서 자기공명영상장치를 이용한 확산계수 측정에 대한 기초 연구)

  • Mun Chi-Woong;Choi, Ki-Sueng;Nana Roger;Hu, Xiaoping P.;Yang, Young-Il;Chang Hee-Kyung;Eun, Choong-Ki
    • Journal of Biomedical Engineering Research
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    • v.27 no.5
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    • pp.203-209
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    • 2006
  • The aim of this study is to investigate the feasibility of ex vivo MR diffusion tensor imaging technique in order to observe the diffusion-contrast characteristics of human gastric tissues. On normal and pathologic gastric tissues, which have been fixed in a polycarbonate plastic tube filled with 10% formalin solution, laboratory made 3D diffusion tensor Turbo FLASH pulse sequence was used to obtain high resolution MR images with voxel size of $0.5{\times}0.5{\times}0.5mm^3\;using\;64{\times}32{\times}32mm^3$ field of view in conjunction with an acquisition matrix of $128{\times}64{\times}64$. Diffusion weighted- gradient pulses were employed with b values of 0 and $600s/mm^2$ in 6 orientations. The sequence was implemented on a clinical 3.0-T MRI scanner(Siemens, Erlangen, Germany) with a home-made quadrature-typed birdcage Tx/Rx rf coil for small specimen. Diffusion tensor values in each pixel were calculated using linear algebra and singular value decomposition(SVD) algorithm. Apparent diffusion coefficient(ADC) and fractional anisotropy(FA) map were also obtained from diffusion tensor data to compare pixel intensities between normal and abnormal gastric tissues. The processing software was developed by authors using Visual C++(Microsoft, WA, U.S.A.) and mathematical/statistical library of GNUwin32(Free Software Foundation). This study shows that 3D diffusion tensor Turbo FLASH sequence is useful to resolve fine micro-structures of gastric tissue and both ADC and FA values in normal gastric tissue are higher than those in abnormal tissue. Authors expect that this study also represents another possibility of gastric carcinoma detection by visualizing diffusion characteristics of proton spins in the gastric tissues.

Effect of Amoxicillin on the Intestinal Membrane Permeability and Absorption Clearance of Benazepril (베나제프릴의 장관막 투과도와 흡수 클리어런스에 미치는 아목시실린의 영향)

  • Joo, Eun-Hee;Kim, Young-Man;Ko, Hyung-Seok;Lee, Yong-Bok;Na, Han-Kwang
    • Journal of Pharmaceutical Investigation
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    • v.28 no.1
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    • pp.25-33
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    • 1998
  • Intestinal absorption of ${\beta}-lactam$ antibiotics and angiotensin converting enzyme(ACE) inhibitors has been shown to use the carrier-mediated transport system. In vitro experiments have established that the efficacy of uptake by enterocytes depends on an inwardly directed proton gradient. It was suggested that benazepril was mediated by tripeptide transport system and that amoxicillin was transported by dipeptide transport carrier. The aim of this study is to assess the influence of amoxicillin on the intestinal absorption of benazepril using in vitro diffusion chamber and in situ single pass perfusion technique in the rat in order to elucidate whether the above transport systems are competitive or not. We obtained the gastrointestinal pemeability coefficient of amoxicillin, benazepril and both of them using in vitro diffusion chamber. And also the gastrointestinal absorption clearance of amoxicillin, benazepril and both of them using in situ single-pass perfusion method at steady state were calculated. Amoxicillin and benazepril were analyzed by HPLC. The results by the use of diffusion chamber in vitro indicated that the apparent intestinal permeability coefficient of benazepril was significantly(p<0.01) decreased by amoxicillin(45.2%) and vice versa significantly(p<0.01) decreased(89.1%). The results by the in situ gastrointestinal single-pass perfusion method indicated that the intestinal absorption clearance of benazepril was significantly(p<0.05) decreased by amoxicillin (40.2%) and vice versa significantly(p<0.05) decreased(54.8%). These results might suggest that they share the same peptide carrier pathway for oral absorption.

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Effect of Support on the Performance and Electrochemical Durability of Membrane in PEMFC (PEMFC의 고분자막에서 지지체가 고분자전해질 막 성능 및 전기화학적 내구성에 미치는 영향)

  • Oh, Sohyung;Lim, Dae Hyun;Lee, Daewoong;Park, Kwonpil
    • Korean Chemical Engineering Research
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    • v.58 no.4
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    • pp.524-529
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    • 2020
  • To increase the mechanical durability of the proton exchange membrane fuel cells, a reinforced membrane in which a support is placed in the polymer membrane is used. The support mainly uses e-PTFE, which is hydrophobic and does not transfer ions, which may cause performance degradation. In this study, we investigated the effect of e-PTFE support on PEMFC performance and electrochemical durability. In this study, the reinforced membrane with the support was compared with the single membrane (non-reinforced membrane). Due to the hydrophobicity of the support, the water diffusion coefficient of the reinforced membrane was lower than that of the single membrane. The reinforced membrane had a lower water diffusion coefficient, resulting in higher HFR, which is the membrane migration resistance of ions, than that of a single membrane. Due to the low hydrogen permeability of the support, the OCV of the reinforced membrane was higher than that of the single membrane. The support was shown to reduce the hydrogen permeability, thereby reducing the rate of radical generation, thereby improving the electrochemical durability of the reinforced membrane.

Electrochemical Behavior of a Nickel Hydroxide Particle for Ni-MH Battery by Microelectrode (마이크로전극에 의한 니켈수소전지용 수산화니켈 입자의 전기화학적 거동)

  • Kim, Ho-Sung;Oh, Ik-Hyun;Lee, Jong-Ho
    • Journal of the Korean Electrochemical Society
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    • v.10 no.2
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    • pp.145-149
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    • 2007
  • Electrochemical studies were performed for a single particle of nickel hydroxide for the cathode of Ni-MH batteries. A carbon fiber microelectrode was manipulated to make electrical contact with an alloy particle, and electrochemical experiments were performed. As a result of cyclic voltammetry, the oxidation/reduction and oxygen evolution reaction (OER) are clearly separated for a single particle. The total cathodic charge (Qred) is practically constant for the scan rate investigated, indicating that the whole particle has reacted. The total anodic charge(Qox) was larger than that of reduction reaction, and the magnitude of oxygen evolution taking place as a side reaction was enhanced at lower scan rates. As a result of galvanostatic charge and discharge measurement, the discharge capacity of single particle was found to be 250 mAh/g, value being very close to the theoretical capacity (289 mAh/g). The apparent proton diffusion coefficient(Dapp) using potential step method inside the nickel hydroxide was found to range within $3{\sim}4{\times}10^{-9}\;cm^2/s$.

Micelle Formation of Surfactant Solution(3) -Self-Diffusion and 1H Relaxation for Mixed Micelle of Nonionic and Ionic Surfactants- (계면활성제 수용액에서 미셀형성(제3보) -비이온성과 이온성계면활성제의 혼합 미셀에 있어 자기확산 및 프로톤 이완-)

  • Choi, Seung-Ok;Kwack, Kwang-Soo;Park, Heung-Jo;Nam, Ki-Dae
    • Applied Chemistry for Engineering
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    • v.10 no.6
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    • pp.876-880
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    • 1999
  • The surfactant self-diffusion coefficients of mixed micellar solutions of ionic and nonionic surfactants have been measured by the NMR pulsed field gradient spin echo(FT-PGSE) method. In addition, the line widths of $^1H$ NMR signal have been monitored. The system investgated are $C_{12}EO_5/SDS/D_2O$, $C_{12}EO_5/DTAC/D_2O$, and $C_{12}EO_8/SDS/D_2O$. In the sample series, the molar ratios of $D_2O$ to surfactant(ionic+nonionic) were kept constant while the surfactant mixing ratio was varied. For the $C_{12}EO_5$ system, the surfactant self-diffusion coefficient indicates minimum when the surfactant mixing ratio is about 20% ionic surfactant. The observed decrease in self-diffusion coefficients as nonionic surfactant was replaced by ionic surfactant is interpreted to mainly be due to an increased micelle-micelle repulsion. The increase in self-diffusion coefficients occurring at higher fraction of ionic surfactant is shown to be due to a decrease in micelle size. For the $C_{12}EO_8$ system, the effect of the surfactant mixing ratio is much weaker which can be understood by considering the molecular geometry and large headgroup area. The proton NMR line widths correlate well with the self-diffusion coefficients and broadening of the alkyl chain methylene signals is found when the self-diffusion coefficients is low.

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Poly(vinyl alcohol) Membranes Containing Sulfonic Acid Groups for Direct Methanol Fuel Cell Application (설폰산기를 함유한 PVA막의 직접 메탄올 연료전지 응용)

  • Lee Young Moo;Lee Sun Yong
    • Membrane Journal
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    • v.14 no.3
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    • pp.240-249
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    • 2004
  • Crosslinked PVA membranes were achieved by esterification between the hydroxyl groups of PVA and carboxyl group of sulfosuccinic acid (SSA). SSA containing sulfonic group was used as a chemical crosslinking agent as well as a donor of fixed anionic group ($-SO_3$H). The crosslinking density of membranes was controlled by SSA content and calculated using polar and non-polar solvent. The crosslinking density measured by using non-polar solvent such as xylene and benzene increases with SSA content. However, using the polar solvent such as water and methanol, the crosslinking density increases up to SSA content of 20 wt% and above the content decrease due to sulfonic acid groups. The crosslinked PVA membranes were studied in relation with water diffusion coefficient and mechanical property as well as proton conductivity and methanol permeability as a function of crosslinking density. These properties were all dependent on the effect of SSA content.