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Kim, Woonjung,Bae, Jihyun,Eum, Chul Hun,Jung, Jongjin,Lee, Seungho Elsevier 2018 Microchemical journal Vol.142 No.-
<P><B>Abstract</B></P> <P>Carbon black (CB) has excellent chemical and physical properties including strong chemical strength and electrical conductivity. CB is widely used in various industries such as semiconductor, tire, rubber, ink, paint, toner and resin. When used in ink, as the CB particle size and the size distribution become smaller and narrower, respectively, they tend to be better dispersed, and the glossiness and stability of the ink increases.</P> <P>In the present study, asymmetrical flow field-flow fractionation (AsFlFFF) was employed to analyze the size distribution of CB particles used in ink. CB suspensions were prepared by dispersing CB powder in aqueous media containing copolymeric dispersing agents of hydrophobic (styrene) and hydrophilic (acrylic or maleic acid) monomers. Experimental parameters of AsFlFFF were optimized for analysis of the CB particles.</P> <P>Although the mean sizes obtained by AsFlFFF and dynamic light scattering (DLS) were in good agreements for those with narrow size distributions, DLS failed to distinguish among the CB suspensions having broad size distributions, whereas AsFlFFF differentiated them easily. Results indicated that the CB particles were dispersed better with copolymeric dispersing agents having an aromatic polymer with OH functionality than those with COOH functionality. It was also observed that, as the mean size of the CB particles decreases and the size distribution becomes narrower, the ink become thermally more stable.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Aromatic polymers having high thermal stability were synthesized for surface modification of carbon black (CB) particles. </LI> <LI> Asymmetric flow field-flow fractionation (AF4) was employed for characterization of surface modified CB particles. </LI> <LI> DLS failed to distinguish CB suspensions having broad size distributions, whereas AsFlFFF was able to differentiate. </LI> <LI> CB particles were dispersed better with dispersing agents with OH functionality than those with COOH. </LI> </UL> </P>
Kim, Kihyun,Choi, Seong-Ho,Lee, Seungho,Kim, Woonjung The Korean Society of Analytical Science 2019 분석과학 Vol.32 No.5
As the size of semiconductors becomes smaller, it is necessary to perform high precision polishing of nanoscale. Ceria, which is generally used as an abrasive, is widely used because of its uniform quality, but its stability is not high because it has a high molecular weight and causes agglomeration and rapid precipitation. Such agglomeration and precipitation causes scratches in the polishing process. Therefore, it is important to accurately analyze the size distribution of ceria particles. In this study, a study was conducted to select dispersants useful for preventing coagulation and sedimentation of ceria. First, a dispersant was synthesized and a ceria slurry was prepared. The defoamer selection experiment was performed in order to remove the air bubbles which may occur in the production of ceria slurry. Dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) were used to determine the size distribution of ceria particles in the slurry. AsFlFFF is a technique for separating nanoparticles based on sequential elution of samples as in chromatography, and is a useful technique for determining the particle size distribution of nanoparticle samples. AsFlFFF was able to confirm the presence of a little quantities of large particles in the vicinity of 300 nm, which DLS can not detect, besides the main distribution in the range of 60-80 nm. AsFlFFF showed better accuracy and precision than DLS for particle size analysis of a little quantities of large particles such as ceria slurry treated in this study.
Kim, Kihyun,Lee, Seungho,Kim, Woonjung The Korean Society of Analytical Sciences 2019 분석과학 Vol.32 No.3
High viscosity carbon black dispersions are used in various industrial fields such as color cosmetics, rubber, tire, plastic and color filter ink. However, carbon black particles are unstable to heat due to inherent characteristics, and it is very difficult to keep the quality of the product constant due to agglomeration of particles. In general, particle size analysis is performed by dynamic light scattering (DLS) during the dispersion process in order to select the optimum dispersant in the carbon black dispersion process. However, the existing low viscosity analysis provides reproducible particle distribution analysis results, but it is difficult to select the optimum dispersant because it is difficult to analyze the reproducible particle distribution at high viscosity. In this study, dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) analysis methods were compared for reproducible particle size analysis of high viscosity carbon black. First, the stability of carbon black dispersion was investigated by particle size analysis by DLS and AsFlFFF according to milling time, and the validity of analytical method for the selection of the optimum dispersant useful for carbon black dispersion was confirmed. The correlation between color and particle size of particles in high viscosity carbon black dispersion was investigated by using colorimeter. The particle size distribution from AsFlFFF was consistent with the colorimetric results. As a result, the correlation between AsFlFFF and colorimetric results confirmed the possibility of a strong analytical method for determining the appropriate dispersant and milling time in high viscosity carbon black dispersions. In addition, for nanoparticles with relatively broad particle size distributions such as carbon black, AsFlFFF has been found to provide a more accurate particle size distribution than DLS. This is because AsFlFFF, unlike DLS, can analyze each fraction by separating particles by size.
Polymer brush: a promising grafting approach to scaffolds for tissue engineering
( Woonjung Kim ),( Jongjin Jung ) 생화학분자생물학회(구 한국생화학분자생물학회) 2016 BMB Reports Vol.49 No.12
Polymer brush is a soft material unit tethered covalently on the surface of scaffolds. It can induce functional and structural modification of a substrate`s properties. Such surface coating approach has attracted special attentions in the fields of stem cell biology, tissue engineering, and regenerative medicine due to facile fabrication, usability of various polymers, extracellular matrix (ECM)-like structural features, and in vivo stability. Here, we summarized polymer brush-based grafting approaches comparing self-assembled monolayer (SAM)-based coating method, in addition to physico-chemical characterization techniques for surfaces such as wettability, stiffness/ elasticity, roughness, and chemical composition that can affect cell adhesion, differentiation, and proliferation. We also reviewed recent advancements in cell biological applications of polymer brushes by focusing on stem cell differentiation and 3D supports/implants for tissue formation. Understanding cell behaviors on polymer brushes in the scale of nanometer length can contribute to systematic understandings of cellular responses at the interface of polymers and scaffolds and their simultaneous effects on cell behaviors for promising platform designs. [BMB Reports 2016; 49(12): 655-661]