• Journal of Adhesion and Interface
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• v.24 no.4
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• pp.131-135
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• 2023

Lecithin self-assembles into reverse spherical micelles in organic solvents as an amphiphilic molecule. When additives such as bile salts and water are introduced into lecithin solutions, it induces structural changes in the molecular form of lecithin, leading to the transformation into reverse cylindrical micelles. In this study, we observe the rheological changes of lecithin/bile salt mixtures in a decane system after the addition of water. The resulting mixtures exhibit high viscosity and characteristics of viscoelasticity, suggesting potential applications in various fields such as drug delivery and edible oil gels.

• Journal of Microbiology and Biotechnology
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• v.34 no.4
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• pp.891-901
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• 2024

This study focuses on improving the 3D printability of pea protein with the help of food inks designed for jet-type 3D printers. Initially, the food ink base was formulated using nanocellulose-alginate with a gradient of native potato starch and its 3D printability was evaluated. The 3D-printed structures using only candidates for the food ink base formulated with or without potato starch exhibited dimensional accuracy exceeding 95% on both the X and Y axes. However, the accuracy of stacking on the Z-axis was significantly affected by the ink composition. Food ink with 1% potato starch closely matched the CAD design, with an accuracy of approximately 99% on the Z-axis. Potato starch enhanced the stacking of 3D-printed structures by improving the electrostatic repulsion, viscoelasticity, and thixotropic behavior of the food ink base. The 3D printability of pea protein was evaluated using the selected food ink base, showing a 46% improvement in dimensional accuracy on the Z-axis compared to the control group printed with a food ink base lacking potato starch. These findings suggest that starch can serve as an additive support for high-resolution 3D jet-type printing of food ink material.

• Journal of the Korean Society of Visualization
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• v.22 no.2
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• pp.63-73
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• 2024

The injection of polymer can significantly reduce drag, particularly in the turbulent flow region where the mutual interaction between the polymer and turbulent vortices occurs. In this study, Taylor-Couette flow of PEO-in-water solutions with a rotating inner cylinder was analyzed. Despite the shear-thinning behaviour of PEO-in-water solutions being well-documented, for a given range of shear rates their viscosity remains nearly constant. By varying the polymer concentration, we analyzed the torque evolution of different solutions followed by the viscoelasticity effects of the polymer on the interphase transition points. The torque was analyzed using a dimensionless torque scaling method, which allows for the assessment of the fluid's momentum transport capabilities. It was observed that for low concentrations of PEO, the flow behaviour exhibited only minor differences in comparison to that of water, the Newtonian fluid. However, once the PEO concentration exceeded the polymer overlap concentration, the flow behaviour was significantly altered.

• Polymer(Korea)
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• v.32 no.2
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• pp.116-124
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• 2008

A commercialized biobased and biodegradable poly(lactic acid)(PLA) containing the functional monomer of glycidyl methacrylate (GMA) was chemically modified using reactive extrusion to enhance its melt strength. Modified PLAs were prepared with various contents of GMA and initiator, and were characterized by observing their gel fraction, thermal properties, melt viscoelasticity and biodegradability. The complex viscosity and storage modulus of chemically modified PLA with the initiator alone was increased by addition of initiator and were more increased in the presence of GMA. There was a optimum content of GMA showing the maximum complex viscosity with the amount of initiator. The biodegradebility of modified PLA was slightly decreased by addition of GMA.

• Journal of the East Asian Society of Dietary Life
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• v.22 no.5
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• pp.684-691
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• 2012

Glutinous rice dduk, traditional Korean rice cake, was prepared using rice(white glutinous rice, brown glutinous rice, black glutinous rice, gaba glutinous rice) as a meal alternative, and each of their quality characteristics were compared. This study had checked sensory tests, color differences, moisture contents, texture characteristics, and storage lives of dduk during storage at room temperature for 6 days. The moisture contents of black glutinous rice dduk scored the highest. For color properties, gaba glutinous rice dduk was darker with a decreased yellow value, whereas its red value was higher comparing with that of brown glutinous rice dduk. The results of the preference test showed that appearance, flavor, texture, and overall preference were the highest in white glutinous rice dduk, whereas black glutinous rice dduk showed the lowest score. The results of the color difference test showed that softness, viscoelasticity, and fineness were the highest in white glutinous rice dduk, whereas black glutinous rice dduk showed the highest difference in color. For individual textural characteristics, black glutinous rice dduk showed the highest score, whereas white glutinous rice dduk showed the lowest scores in hardness, chewiness, and gumminess. In the results of the textural characteristics of dduk during storage, white glutinous rice dduk showed the highest increase in hardness after 48 hours, whereas black glutinous rice dduk showed the lowest increase. White glutinous rice dduk showed the highest increases in chewiness and gumminess. Cohesiveness decreased in all glutinous rice dduk. In the results of fungal occurrence in dduk during storage, black and gaba glutinous rice dduk showed increased fungi occurrence compared with white and brown glutinous rice dduk after 6 days. In conclusion, the overall preference for glutinous rice dduk made from different rice is more affected by appearance or texture than flavor.

• Journal of the Korean Applied Science and Technology
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• v.33 no.3
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• pp.540-548
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• 2016

The non-Newtonian flow curves of sodium bis-(2-ethylhexyl)sulfosuccinate-water lamellar liquid crystals were obtained in various concentrations and temperatures by using a cone-plate rheometer. By applying non-Newtonian flow equation to the flow curves for AOT-water lamellar liquid crystal samples, the rheological parameters were obtained. Particular attention is given to the hysteresis loop detected when the liquid crystal samples are shear under increasing-decreasing shear stress modes which result in thixotropic and dilatant behavior. Sodium bis-(2-ethylhexyl)sulfosuccinate-water lamellar liquid crystals behave as weak gels when they are subjected to shear flow, but when the applied stress surpasses the yield stress, they exhibit non-linear viscoelasticity. Upon decreasing shear rate, the dispersion still preserves much of its structure and consequently its shear stress remains higher than the values measured in the increasing shear rate mode.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.6
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• pp.26-32
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• 2015

In this study, it is evaluated for fracture toughness to analyze crack resistance properties of particulate reinforced composite propellant. Fracture toughness test using WST specimen is conducted by temperature conditions from $50^{\circ}C$ to $-60^{\circ}C$. Evaluation method for fracture toughness calculated using an equation suggested by ASTM E399 with linear elastic fracture mechanics. From these result, splitting loads and stress intensity factors of propellant increase according to decrease of test temperature. Also, the strain fields of specimen surface using digital image correlation increase as temperature decreased from $50^{\circ}C$ to $-40^{\circ}C$, but it sharply decreases at $-60^{\circ}C$ because of brittle behavior.

• Macromolecular Research
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• v.17 no.5
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• pp.332-338
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• 2009

Rheological behavior of natural hydrogel produced from seeds of three Salvia spp. (S. miltiorrhiza (SM), S. sclarea (SS), S. viridis (SV)) was investigated by using a Rheometer equipped with a cone and plate geometry measuring system under never-dried condition. Different chemical contents of such hydrogels give significant effects on their rheological properties. Because of incomplete penetration of water inside the hydrogels after drying before-dried hydrogels were used for rheological analysis. To know molecular interactions which predominated in the gel formation, some constituents were externally added to the 1.0% (w/w) hydrogel. Addition of urea to disrupt hydrogen bonds reduced 3.4-67% viscosity of the untreated hydrogels and changed viscoelastic properties from gel to liquid-like behavior. Neutral salts added to the hydrogel solution at 0.1 M also lowered the viscosity in a manner related with increase in size of cations and temperature. Changing from gel state to liquid-like state was also easily confirmed by oscillation measurement (storage, G', and loss, G", modulii) typically observed in the cases of potassium sulfate and potassium thiocyanate. Influence of pH variation on the viscosity explained that weak alkaline condition (pH 8-9) creates a higher resistance to flow due to increasingly electrostatic repulsions between negative charges ($COO^-$) Importance of calcium bridges was also demonstrated by recovery of viscosity of the hydrogels by addition of calcium after acidification. The summarized results indicate that electrostatic repulsion is a major contributor for production of hydrogel structure.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.6
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• pp.717-726
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• 2005

Statement of problem. One of the common problems of provisional crown and fixed partial denture materials is that when they are subjected to constant loads for a long period of time, they exhibit a dimensional change (creep). Purpose. The aim of this study was to investigate the viscoelastic behaviour of polymer-based provisional crown and fixed partial denture materials with time at constant compressive load. Material and methods. Three dimethacrylate-based materials (Protemp 3 Garant, Temphase, Luxatemp) and one monomethacrylate-based material (Trim) were selected. Dimensional changes of the specimens were recorded by a LVDT to evaluate their viscoelastic behavior and creep strain. For all specimens, two loading procedures were used. At first, static compressive stress of 4 MPa was applied for 30 minutes and followed by 1 hour of strain recovery. Then, after 24 hours of water storage, the specimens were loaded again. The creep values between materials were statistically analyzed using one-way ANOVA and multiple comparison $Scheff\acute{e}$ test. Independent samples t-test was also used to identify the difference of creep strain between first and secondary loading conditions at the significance level of 0.05. Results. Following application of the first loading, Trim showed the highest maximum creep strain (32.7%) followed by Luxatemp, Protemp 3 Garant and Temphase, with values of 3.78%, 2.86% and 1.77%, respectively. Trim was significantly different from other materials (P<0.05), while there were no significant differences among Luxatemp, Protemp 3 Garant and Temphase (P>0.05). The highest recovery and permanent set of Trim, were significantly different from those of others (P<0.05). At the secondary loading of the dimethacrylate-based materials, creep deformation, recovery and permanent set decreased and the percentage of recovery increased, while in Trim, all values of the measurements increased. This result showed that the secondary loading at 24 hours produced a significant creep magnitude. Conclusion. The dimethacrylate-based provisional crown and fixed partial denture materials showed significantly higher creep resistance and lower deformation than the monomethacrylate-based material. Thus, monomethacrylate-based materials should not be used in long-term stress-bearing situations.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.2
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• pp.220-229
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• 2001

This study was performed to evaluate the fracture resistance of three improved die stone materials according to water/powder ratio. There are lots of handling conditions which affect the physical properties of improved dental stone, and it's well known that the water/powder ratio significantly affect the strength of die stone. If water/power ratio was incorrect, following disadvantages were showed : (1) susceptibility to dimensional change due to abrasion, (2) limited reproduction of fine detail, (3) lack of strength. The maxillary master casts were made of additional silicone impressions(Exaflex, GC America. Inc. USA). Three type IV die stones such as Fuji Rock (GC Europe Intreleuvenlaan, Leuven, Belgium), Velmix(Kerr, Manufacturing company, USA), and Crytal Rock( Maruishi Gypsum Co. Ltd, Japan) were tested. A total of 160 casts were prepared, separated, and tested on the Instron Testing Machine(Model 4201, Co. USA). The obtained results of this study were as follows : 1. Fuji Reck and Velmix less 3ml than the water/power ratio of manufacturer's instruction showed the highest resistance to fracture. According to increasing water/powder ratio, fracture resistance was significantly increased(P<0.05). Crystal Rock showed the highest fracture value when it was mixed with the water/power ratio of manufacturer's instruction. 2. Water/powder ratio of the manufacturer's instructions and less 3ml than that showed lower fracture value of hand mix than that of vacuum mix. Water/powder ratio of more 3ml, 6ml than manufacturer's instructions was not significantly different between hand mix and vacuum mix(p>0.05). 3. Velmix had the highest viscoelastic value among three die materials when it was mixed with the manufacturer's instruction. Viscoelasticity was decreased according to increasing water/powder ratio.