Nonhydrodynamic Translational Diusion of a Coarse-Grained Wormlike Polyelectrolyte Chain Conned in Nanochannels by Using Brownian Dynamics Simulations

전명석 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

A coarse-grained model of semiflexible anionic polyelectrolyte xanthan is applied and its structure and dynamics are examined with Brownian dynamics(BD) simulations both in a bulk solution and under confinement between two parallel plates. The modeling is based on the nonlinear bead-spring discretization of a chain with additional long-range electrostatic and hydrodynamic interactions between pairs of beads. Neutral and negatively-charged glass surfaces are combined to make three kinds of slit channels with different charge characteristics as neutral-neutral, glass-glass and neutral- glass walls, where uniform conditions of the surface charge density are assumed. Simulation parameters are obtained from previously reported rheology data on the native and sonicated xanthan polysaccharides. The structural transition of the chain and its dependence on the Debye screening of the electrolyte solution are characterized. The wall charge effect is found to be significant as the ionic strength decreases, where a strongly-charged glass wall strengthens the effective confinement ofxanthan. A nonmonotonic variation of chain size with changing slit width is also observed in the neutral slit. An asymmetrically-charged slit can induce xanthan migration toward a less repulsive wall and a narrow-down of the chain distribution across the channel, suggesting the usefulness of surface treatment of channel walls to manipulate polyelectrolytes. We need to point out that the scaling law developed for neutral polymers is limited for direct application to polyelectrolytes.

Water Sorption and Hindered Diffusion with Different Chain Stiffness of Superabsorbent Polymer

전명석,이대영 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.1

Water sorption and diffusion are essential physicochemical properties of a high-performance superabsorbent polymer (SAP). We combine the Park model with the obstruction-scaling model and the water clustering in confined spaces of the polymer hydrogel. Special attention is focused on elucidating the effect of chain stiffness by considering the conformation of the polymer chain. Theoretical model parameters are determined from the best fits by simultaneous nonlinear regressions for both sorption and corrected diffusion data based on previous experiments with poly(acrylamide-co-sodium acrylate) hydrogel. Predictions show that the hindered water diffusivity leads to a sigmoid curve with relative humidity aw, where it increases monotonically up to aw ≈ 0.6 due to the swelling but decreases at higher aw caused by water clustering. Water diffusion decreases with increasing chain stiffness, and the larger persistence length provides a smaller opening radius in void spaces regarding the weak elastic deformation of hydrogel under the applied stress.

투과플럭스 실험으로부터 콜로이드 서스펜션의 삼투압과 입자의 구배확산계수 산출을 위한 수치적 해석

전명석 한국막학회 2002 멤브레인 Vol.12 No.2

멤브레인 여과 실험에서 얻어진 데이터 처리에 간단한 수치해석을 적용하여 삼투압(osmotic pressure) 과 구배확산계수(gradient diffusion coefficient)를 도출하는 새로운 방법론을 제시하였다. 삼투압과 구배확산계수는 이론 및 실험적으로 쉽게 구할 수 없는 물리적 특성치로서 멤브레인 여과의 특성 규명에 중요하다. 모델 라텍스 콜로이드의 여과시간에 따른 투과플럭스(permeate flux) 값과 이에 대한 수치적분과 수치미분 데이터로부터 분산된 입자농도의 함수인 삼투압 관계식을 구했다. 이로부터 계산된 열역학적 계수(thermodynamic coefficient)는 입자농도가 증가할수록 감소하는 거동을 보였고, 여기에 기존에 제시되어 있는 수력학적 계수(hydrodynamic coefficient)를 도입하여 구배확산계수를 산출하였다. 아울러, 본 연구에서 계산된 입자농도에 따른 구배확산계수의 결과와 동일한 멤브레인과 라텍스 콜로이드의 여과에 대해서 기존에 통계역학적 시뮬레이션으로 예측한 결과를 비교하였다. A novel methodology on the calculations of osmotic pressure and gradient diffusion coefficient has been provided ill the present study, by applying a succinct numerical analysis on the experimental results. Although both the osmotic pressure and the gradient diffusion coefficient represent a fundamental characteristic in related membrane filtrations such as microfiltration and ultrafiltration, neither theoretical analysis nor experiments can readily determine them. The osmotic pressure of colloidal suspension has been successfully determined from a relationship between the data of the time-dependent permeate flux, their numerical accumulations, and their numerical derivatives. It is obvious that the osmotic pressure is gradually increased, as the particle concentration increases. The thermodynamic coefficient was calculated from the numerical differentiation of the correlation equation of osmotic pressure, and the hydrodynamic coefficient was evaluated from the previously developed relation for an ordered system. Finally, the estimated gradient diffusion coefficient, which entirely depends on the particle concentration, was compared to the previous results obtained from the statistical mechanical simulations.

농협의 불법행위책임에 관한 연구

전명석 농협대학교 협동조합경영연구소 2003 협동조합경영연구 Vol.29 No.-

The purpose of this study is to investigate the liability of the Agricultural Cooperative fo tort. The Cooperative and The Federation shall be a juridical person. the agricultural cooperative possesses property, and reason that has right and duty through these representative organization’s expression. The agricultural cooperative has conducted various activitis in the development of the national economy, and makes contributions in intricate modern socity. On the other hand, it does damage to diverse fields of society in performing its functions. The Article 35 of Civil Law prescribes the liablity of juridical person for tort. The important contents are summarised as follows; Firstly, the legal personality of agricultural Cooperative is a corporation of juridical persons, a nonprofit making corporation, and a middle of the juridical person. Secondly, under the Article 35 of civil law, seeking for the safety of dealing and the protection for others by interpreting on business in keeping with the external theories which help to widen the extent of juridical person’s liability. Thirdly, The officers of the representative organization shall be jointly responsible for the compensation of any damage incurred to third person in carrying out his duties.

일반적 Helmholtz-Smoluchowski 원리에 따른 중공사 미세기공 채널에서의 계면동전기 흐름전위에 관한 실험연구

전명석,조홍일 한국막학회 2002 멤브레인 Vol.12 No.1

하전된 마이크로채널의 전기이중층에서 계면동전기 흐름에 의해 발생되는 흐름전위는 일반적 Helmholtz-Smoluchowski 관계식으로부터 중공사 멤브레인 기공의 제타전위를 결정하는데 적용된다. 흐름전위는 실제 운전상황이나 물리화학적 조건에서의 표면특성 및 기공과 입자간 상호작용에 대한 유용한 실시간 정보를 제공함이 알려져 있다. 무리화학적 인자들이 주공사에 의한 여과에 미치는 영향을 투과플럭스와 흐름전위의 동시적 모니터링으로 고찰하였다. 특히, 본 연구에서는 중공사의 위치에 따른 흐름전위를 측정함으로써 중공사 길이 방향과 멤부레인 오염 진행에 따라 달라지는 케이크층 효과를 규명하는 실험방법을 다루었다. 실험결과, 입자농도가 증가할수록 투과플럭스는 감소하나 흐름전위는 증가하였다. 입자농도가 증가하면서 케이크층 성장은 활발하지만 쌓인 하전 입자들의 표면전하 효과로 흐름전위는 증가한 것이다. 용액의 이온화 세기를 KCI 0.1 mM에서 10mM로 증가하면 투과플럭스와 흐름전위가 함께 감소하였다. 이는, 이온화 세기의 증가로 라텍스입자 주위의 Debye 길이 감소로 치밀한 케이크층이 형성되고, 전기이중층의 얇아진 확산층에 의한 이온흐름의 약화로 흐름전위는 감소한 것을 판단된다. The streaming potential generated by the electrokinetic flow within electric double layer of charged microchannel is applied to determine the zeta potential of hollow-fiber membrane pore by using the general Helmholtz-Smoluchowski equation. The streaming potential is know to provide a useful real-time information on the surface property and the interaction between pore and particles in actual situations and physicochemical conditions. The influence of physicochemical parameters upon the filtration with hollow-fibers has been examined with an in-situ and simultaneously monitoring the streaming potential as well as permeate flux. In particular, the present study examined an experimental method to identify the effect of cake layer which can vary according to the axial position of a hollow-fiber and the progress of membrane fouling by measuring the position-dependent streaming potential. As the latex concentration increases, the permeate flux decreased but the streaming potential increased. The growth of cake layer has been mire developed with increasing latex concentration, however, the effect of surface charges of latexes deposited on the membrane surface leads to increase the streaming potential. With increasing ionic concentration of KCI, both the permeate flux and the streaming potential decrease. The increase of ionic concentration provides a compact cake layer due to the shrinkage of Debye length and the decreased streaming potential results from the weakened ionic flows owing to a thin diffusive double layer.

상변화물질을 이용한 잠열축열 기술

전명석 한국태양에너지학회 2006 태양에너지 : 한국태양에너지학회지 Vol.5 No.1

P-483 : Nano-Scale Measurements of Long-Range Interactions in Microfluidic Channel Using AFM with Colloidal Particle Probe

전명석,( R. W. Lovitt ),( W. R. Bowen ) 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2

Long-range interactions are important to understand the physicochemical phenomena of electric field in either micro-biochip or MEMS devices confined to the charged solid wall and to analyze the behavior of complex fluids dispersed by either colloids or nanoparticles. Atomic force microscopy (AFM) results were obtained for electrostatic interaction force profiles between a silicon nitride tip and a silica surface by the traditional method as well as between a spherical silica particle and a silica surface employing a colloid probe technique. Distances ranging several tens of nanometers were successfully measured under a contact mode in 1.0 mM KCl electrolyte solution at different pH values. Experimental results obtained by the colloid probe were compared with the calculations from Derjaguin approximation as well as rigorous numerical method. As the separation distance between the silica surface and silica particle is decreased, the approximation under constant potential gives greater interaction than our measured values, with its difference becoming large. AFM results in PDMS-based microfluidic channel are also presented.

Rheological Correlations of Relaxation Time for Finite Concentrated Semiflexible Polyelectrolytes in Solvents

전명석,고민재 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.7

The Rouse-Zimm model based on the polymer dynamics theory allows us to predict the relaxation time of polyelectrolyte dilute solution as a function of intrinsic viscosity. In finite concentrated solutions, the empirical analysis adopted in this study is quite useful to examine the relaxation behavior, noting that proper theories are not well-clarified and experimental measurements are rather complicated. For xanthan biopolymer selected as the polyelectrolyte model of semiflexible chain, we measured rheological properties of shear viscosity and first normal stress difference in dilute and semidilute solutions over a wide range of shear rate. Power-law scaling relations are commonly observed in the region of shear rate above 1 s<SUP>-1</SUP>. Accurate regressions on shear rate and first normal stress difference present empirical plots as functions of shear rate and xanthan concentration, from which each of relevant fitting parameters are determined. Empirically determined curves are well agreed with the experimental data, ensuring that the empirical formula of characteristic relaxation time<I> </I>is applicable at dilute and finite concentrations, which has not been reported in the literature. We further interpreted the non-Newtonian fluid behavior over a full range of shear rate by applying the Carreau A constitutive model.

Nano-Scale Measurements of Long-Range Interactions in Microfluidic Channel Using AFM with Colloidal Particle Probe

전명석,( R. W. Lovitt ),( W. R. Bowen ) 한국공업화학회 2004 한국공업화학회 연구논문 초록집 Vol.2004 No.1

투척플럭스 실험으로부터 콜로이드 서스펜션의 삼투압과 입자의 구배확산계수 산출을 위한 수치적 해석

전명석 한국막학회 2002 멤브레인 Vol.12 No.2

A novel methodology on the calculations of osmotic pressure and gradient diffusion coefficient has been provided in the present study, by applying a succinct numerical analysis on the experimental results. Although both the osmotic pressure and the gradient diffusion coefficient represent a fundamental characteristic in related membrane filtrations such as microfiltration and ultrafiltration, neither theoretical analysis nor experiments can readily determine them. The osmotic pressure of colloidal suspension has been successfully determined from a relationship between the data of the time-dependent permeate flux, their numerical accumulations, and their numerical derivatives. It is obvious that the osmotic pressure is gradually increased, as the particle concentration increases. The thermodynamic coefficient was calculated from the numerical differentiation of the correlation equation of osmotic pressure, and the hydrodynamic coefficient was evaluated from the previously developed relation for an ordered system. Finally, the estimated gradient diffusion coefficient, which entirely depends on the particle concentration, was compared to the previous results obtained from the statistical mechanical simulations.&enote; 멤브레인 여과 실험에서 얻어진 데이터 처리에 간단한 수치해석을 적용하여 삼투압(osmotic pressure)과 구배확산계수(gradient diffusion coefficient)를 도출하는 새로운 방법론을 제시하였다. 삼투압과 구배확산계수는 이론 및 실험적으로 쉽게 구할 수 없는 물리적 특성치로서 멤브레인 여과의 특성 규명에 중요하다. 모델 라텍스 콜로이드의 여과시간에 따른 투과플럭스(permeate flux) 값과 이에 대한 수치적분과 수치미분 데이터로부터 분산된 입자농도의 함수인 삼투압 관계식을 구했다. 이로부터 계산된 열역학적 계수(thermodynamic coefficient)는 입자농도가 증가할수록 감소하는 거동을 보였고, 여기에 기존에 제시되어 있는 수력학적 계수(hydrodynamic coefficient)를 도입하여 구배확산계수를 산출하였다. 아울러, 본 연구에서 계산된 입자농도에 따른 구배확산계수의 결과와 동일한 멤브레인과 라텍스 콜로이드의 여과에 대해서 기존에 통계역학적 시뮬레이션으로 예측한 결과를 비교하였다.