Biomedical subjects

SJ Park

Publications and source records attributed to SJ Park.

18 recordsLinked to original sources

PubMed2000

Role of Chemically Modified Carbon Black Surfaces in Enhancing Interfacial Adhesion between Carbon Black and Rubber in a Composite System.

The surface and adsorption characteristics of carbon blacks treated with H(3)PO(4), KOH, and C(6)H(6) were investigated. The equilibrium spreading pressure (pi(e)), surface energy (gamma(s)), and specific surface area (S(BET)) were studied by the BET method with N(2) adsorption. In this work, an interpretation based on the nitrogen amount adsorbed for filling a monolayer (a(0)) was proposed for the determination of the Gibbs free energy of nitrogen adsorption, allowing evaluation of the equilibrium spreading pressure or London dispersive component of the surface free energy of the carbon blacks studied. Also, the microstructures of the carbon blacks treated were investigated by transmission electron microscopy. Acidic treatment led to significant decreases in adsorption amount, S(BET), and surface free energy of the carbon blacks, due to aggregation of the microstructures and increasing weight of the swollen specimen in an equilibrium state. Polar basic and nonpolar chemical treatments resulted in an increase of the equilibrium spreading pressure or London dispersive component of surface free energy of the carbon blacks without significantly changing the surface and adsorption properties and microstructures. Results from the surface energetics and parameter of polymer-filler interaction (chi) showed that the tearing energy of the composites is greatly dependent on the carbon blacks studied in the treatment. Copyright 2000 Academic Press.

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PubMed2000

Effect of Fiber-Polymer Interactions on Fracture Toughness Behavior of Carbon Fiber-Reinforced Epoxy Matrix Composites.

The effect of anodic oxidation on high-strength polyacrylonitrile-based carbon fibers has been studied in terms of fiber surface energetics and fracture toughness of the composites. According to contact angle measurements based on the wicking rate of a test liquid, anodic oxidation leads to an increase in surface free energy, mainly due to the increase of its specific (or polar) component. For the carbon-fiber-reinforced epoxy resin matrix system, a direct linear relationship is shown between the specific component and the critical stress intensity factor measured by the single edge notched beam fracture toughness test. From a surface-energetic point of view, the anodic treatment may be suitable for carbon fibers incorporated in a polar organic matrix, resulting in an increased specific component of the surface free energy. Good wetting plays an important role in improving the degree of adhesion at interfaces between fibers and matrices of the resulting composites. Copyright 2000 Academic Press.

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PubMed2000

Studies on Surface Free Energy of an Anhydride-Epoxy Cured System: Effect of Side Alkenyl Chain Length of Hardener on Tensile and Impact Properties.

Three kinds of alkenyl succinic anhydrides (ASA) with varying side chain lengths (2-octenyl, 2-dodecyl, and 2-hexadecynyl succinic anhydrides) for hardeners as epoxy curing agents are synthesized by the ene reaction. The curing effect of ASA on the mechanical tensile and impact properties of cured diglycidyl ether of bisphenol-A (DGEBA) epoxy resin is studied. It is observed that increasing the side alkenyl chain length of ASA leads to a decrease of tensile strength of the cured epoxy resin, probably due to the decreasing of cross-linking density. However, it is found that the impact properties of the casting specimens are increased as the side alkenyl chain length of the hardener increases. This is probably due to the effect of the nonpolar or London-dispersive component of the surface free energy of the ASA studied, resulting in improving of the toughness properties of the casting specimens. Copyright 2000 Academic Press.

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PubMed1999

Dispersive Stabilization of Liquid Crystal-in-Water with Acrylamide Copolymer/Surfactant Mixture: Nematic Curvilinear Aligned Phase Composite Film.

The effect of nonionic surfactant, (H(OCH(2)-CH(2))(8)-OC(6)H(4)-C(9)H(19)), on the dispersion stabilization of liquid crystal (LC)-in-water with acrylamide copolymer containing the related nonylphenyl groups was studied. It was observed that the addition of nonionic surfactant increases the stability of LC dispersions and improves the electrooptical properties of the nematic curvilinear aligned phase (NCAP) composite film. On the basis of the surface tension, reduced viscosity, cloud point, and coalescence time measurements, it was proposed that formation of an integrated structure induced by interactions between hydrophobic groups in the polymer chains is probably important to fabrication of a polymer composite film made of LC and polymer matrix. Copyright 1999 Academic Press.

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PubMed1999

Influence of Anodic Surface Treatment of Activated Carbon on Adsorption and Ion Exchange Properties.

The effect of anodic surface treatment of activated carbon on adsorption and ion exchange characteristics was investigated in the condition of 35 wt% NaOH electrolyte for 60 s. The acid and base values were determined by a titration technique, and surface and pore structures were studied in terms of BET volumetric measurement with N(2) adsorption. The ion exchange capacity of the anodized activated carbons was characterized by a dry weight capacity technique. It was observed that an increase in current intensity leads to an increase in the surface functional groups of activated carbons, resulting in increasing pH, acid-base values, and anion-cation exchange capacities, without significant change of surface and pore structures (i.e., specific surface area, total pore volume, micropore volume, and average pore diameter). Also, anodically treated activated carbons are more effectively evaluated on the base value or cation exchange capacity than on the opposite properties in this electrolytic system. Copyright 1999 Academic Press.

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PubMed1999

Removal of NO over Copper Supported on Activated Carbon Prepared by Electroless Plating.

The effect of copper metal supported on activated carbon on the catalytic reduction of NO has been studied as a short reaction process. It was observed that the adsorption properties of the activated carbons plated with copper metal slightly decrease with an increasing in the plating time or amount of copper metal, within the range of well-developed micropores. The results of reduction show that the presence of copper metal on activated carbon remarkably promotes the NO reduction conversion with the time on stream in the presence of oxygen. But a marginal decrease in the function of plating time is observed. Meanwhile, the NO conversion is almost constant being about 100% after standing 20 h on stream at 500 degrees C in spite of the absence of oxygen. The effects of plating time, experimental temperature, and oxygen amount in the activated carbons have been discussed concerning the NO-copper and/or NO-carbon catalytic reaction. Copyright 1999 Academic Press.

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PubMed1999

XPS Analysis of Carbon Fiber Surfaces-Anodized and Interfacial Effects in Fiber-Epoxy Composites.

High strength carbon fibers were electrochemically treated in an aqueous ammonium carbonate solution, with increasing electric current density, using an original continuous treatment process. The electrochemical treatment induced a modification of the surface properties, i.e., surface functional groups as observed by XPS. As a result, the O1s/C1s and the N1s/C1s ratios of the fiber surfaces increased with the increase of current intensity of the electrochemical treatment in the interval of about 30-50 A m-2. However, no significant change in the surface functional activity characters was observed for strong treatments. Hence, a moderate treatment (30 A m-2) was sufficient to obtain optimum (O1s + N1s)/C1s ratios in this system. This treatment is possibly suitable for carbon fibers to be incorporated in a polar organic matrix, resulting in increasing the interlaminar shear strength (ILSS) of the resulting composites. Copyright 1999 Academic Press.

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PubMed1999

Adsorption Behaviors of CO2 and NH3 on Chemically Surface-Treated Activated Carbons.

The adsorption characteristics of activated carbon treated with 30 wt% HCl and 30 wt% NaOH were investigated. The acid and base values were determined by Boehm's method and the surface structures were studied by the BET method with N2 adsorption and iodine adsorption capacity. Also the adsorption properties of the activated carbons treated with acid and base chemical solutions were investigated with CO2 and NH3 adsorptions. Different adsorption behaviors of CO2 and NH3 on the modified activated carbons were observed, even though the physical surfaces of the activated carbons (i.e., specific surface area, pore size, and pore volume) were not significantly changed. Copyright 1999 Academic Press.

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PubMed1999

Dipyridamole TI-201 SPECT imaging in patients with myocardial bridging

PURPOSE: Exercise-induced myocardial perfusion abnormalities have been reported in patients with myocardial bridging, possibly by tachycardia-induced shortening of diastole. Dipyridamole TI-201 SPECT findings were evaluated in patients with myocardial bridging to assess perfusion abnormalities during dipyridamole stress. MATERIALS AND METHODS: Dipyridamole TI-201 SPECT images of 12 patients with myocardial bridging (> or = 50% systolic narrowing) were evaluated. The peak heart rate during dipyridamole stress was less than 110 beats/min in all patients. The control group was 118 patients with fixed left anterior descending artery (LAD) disease. RESULTS: Fourteen sites of systolic arterial narrowing were present in LAD: two in mid-LAD, seven in distal LAD, and five in septal branches. Dipyridamole TI-201 SPECT showed reversible perfusion defects in three of six sites with 50% to 70% systolic narrowing and seven of eight sites with more than 80% systolic narrowing. Overall, 71% (10 of 14) had a reversible perfusion defect. Five patients with septal branch compression had a perfusion defect in the midanteroseptal wall without an apical abnormality. In the control group, no patient had an isolated perfusion defect in the midanteroseptal wall or septal branch disease (5 of 12 compared with 0 of 118; P < 0.001). CONCLUSIONS: Perfusion abnormalities on dipyridamole TI-201 SPECT are observed in LAD or its branches in patients with high-grade myocardial bridging. Myocardial bridging may decrease coronary flow reserve but not necessarily via tachycardia. Isolated perfusion defects in the midanteroseptal wall may be a characteristic finding of septal branch compression, because a fixed lesion involving a septal branch only is rare.

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PubMed1998

Anodic Surface Treatment on Carbon Fibers: Determination of Acid-Base Interaction Parameter between Two Unidentical Solid Surfaces in a Composite System.

An interpretation based on more precise linear free energy relationships is proposed for the determination of the acid-base interaction of a solid surface, in the context of inverse gas chromatography at infinite dilution. This work leads to the evaluation of acid-base interaction parameter, Ia-b, between two constitutive elements in a composite system. In this work, the acid-base interaction parameters between fibers and matrix are greatly correlated with the results of the interfacial shear strength carried out on single fibers and the interlaminar shear strength of the composites. As an experimental result, electrochemical treatment of fiber surfaces significantly appears essential to the improvement of the acid-base character in a way expected from the nature of the electrolytes used during the treatment. Copyright 1998 Academic Press.

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PubMed1998

Stabilization of Liquid Crystal-in-Water Dispersion with Polymer/Surfactant Mixture: Nematic Curvilinear Aligned Phase Composite Film

The effect of nonionic surfactant (H(OCH2-CH2)8-OC6H4-C9H19) on the stability of liquid crystal-in-water dispersions stabilized by copolymers of acrylamide with hydrophobic monomers have been studied. It was observed that the addition of surfactant increases the stability of liquid crystal (LC) dispersion and improves the electrooptical properties of the nematic curvilinear aligned phase (NCAP) system. According to the interfacial tension measurements, it was proposed that the presence of surfactant allows to form the nonpolar microenvironment in the round of LC droplet and finally reduces the anchoring effect between LC and the polymeric wall. Copyright 1998 Academic Press. Copyright 1998Academic Press

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PubMed1997

Late Clinical Outcome after Intracoronary Palmaz-Schatz Stenting with High Pressure Balloon Dilation without Anticoagulation.

In recent studies, the technique of high pressure balloon dilation for stent optimization has been shown to improve procedural success and to reduce subacute closure after stenting. The late clinical outcome, however, is still uncertain after stenting with high pressure balloon dilation. Therefore, we evaluated the effect of high pressure balloon dilation on the subsequent clinical course in patients after intracoronary stenting. One-hundred ninety patients with 197 lesions were treated with Palmaz-Schatz stent implantation. Intracoronary stenting without high pressure balloon dilation and with anticoagulation was performed in 55 patients with 55 lesions (phase 1), whereas intracoronary stenting with high pressure balloon dilation, without anticoagulation was done in 135 patients with 142 lesions (phase 2). We compared the angiographic and clinical results immediately and at follow-up in both phase 1 and phase 2. Coronary angiography was repeated at 6 months in 147 patients (79%) and 150 lesions (77%). The overall incidence of angiographic restenosis was 24% (31% in phase 1 and 21% in phase 2). Angiographic restenosis occurred in 18% of elective stenting on de novo lesions (23% in phase 1 and 15% in phase 2). The target lesion revascularization rate was 19% (26% in phase 1 and 16% in phase 2). The restenosis rate was significantly reduced with high pressure balloon dilation in the infarct-related artery and for a stent size of ³ 4.0 mm (p < 0.05). In conclusion, intracoronary stenting using high pressure balloon dilation technique without anticoagulation has good immediate results, negligible stent thrombosis and may have a tendency towards lower rates of restenosis.

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PubMed1996