• 폴리머
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• 제38권4호
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• pp.477-483
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• 2014

Poly(lactic acid) (PLA) and poly(${\varepsilon}$-caprolactone) (PCL) blends with various components for melt-blown non-wovens were prepared by a twin-screw extruder. Tributyl citrate (TBC) was added in order to improve the miscibility between PLA and PCL. The results showed that small circular particles of PCL were dispersed in PLA matrix uniformly. The addition of PCL had the heterogeneous nucleation effect on the crystallization of PLA and decreased thermal stability of PLA. The flow of pure PLA and blends approached to Newtonian liquid at a low shear rate and expressed more obvious viscoelasticity at a high shear rate.

• 한국재료학회지
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• 제15권2호
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• pp.112-114
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• 2005

Dispersion stability of the $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles, which was produced by hydrothermal process, was studied in aqueous suspension using ESA (Eletrokinetic Sonic Amplitude). The average particle size of the synthesized $Sm_xCe_{1-x}O_{2-2/x}$ at nanoparticles was about $5{\pm}2nm$. The dispersion and rheological behavior of the $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles aqueous suspension was investigated using $NH_4OH\;and\;HNO_3$ as a disperse agent. The colloidal stability of aqueous suspensions with $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles at different pH values has been investigated by means of zeta potential, average particle size, and the distribution of synthesized $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles. The isoelectric point of the $Sm_xCe_{1-x}O_{2-2/x}$ nanoparticles was at pH around 11 and the value of zeta potential was at its maximum near pH 6.5.

• Korea-Australia Rheology Journal
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• 제11권4호
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• pp.275-278
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• 1999

Soft polymeric materials have gained importance in recent years, namely in food, pharmaceuticals, photographic media, adhesives, vibration dampeners and superabsorbers (to name a few), but also as inter-mediates for selforganization of molecules or supramolecules into long range order. Many of these soft materials are close to their gel point, i.e. they are liquids just before reaching their gel point or they are solids which have barely passed the gel point. New rheological methods need to be developed for the understanding of these soft materials; the typical liquid properties (viscosity) and typical solid properties (modulus) are not applicable since they diverge at the gel point. This will be discussed in the following. Fortunately, chemical gelation experiments with model polymers has given insight into the behavior at the gel point (Winter and Mours, 1997). This knowledge of the critical gel provides us with a reference state when working with soft polymeric materials. Chemical gels will serve as model materials for the exploration of physical gels. A novel method for detecting the gel point has been proposed: the instant of liquid-to-solid transition(gel point) is marked by the crossover of the normalized dynamic moduli G'/cos($n_c$$\pi$/2) and G"/sin($n_c$$\pi$/2).>/2).

• 한국세라믹학회지
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• 제33권6호
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• pp.665-671
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• 1996

Ferroelectric Pb(Fe1/2Nb1/2)O3 thin films were successfully fabricated on ITO/Glass substrate by sol-gel proces-sing and characterized to determine the dielectric and electric properties. Viscosity of PEN sol measured to investigate rheological properties was 3.25 cP which was proper for coating. The sol also showed Newtonian behavior. RTA(Rapid Thermal Annealing) was used for the annealing of the thin film and 1200~1700$\AA$ thick PEN thin films were fabricated by repeating the intermediate and the final annealing. After the deposition of Pt as top electrode by vacuum evaporation dielectric and electric properties were measured. Dielectric properties of FFN thin film were enhanced by increasing the perovskite phase fraction with increasing the annealing temperature. Measured dielectric constant of 1700$\AA$ PFN thin film annealed at $650^{\circ}C$ was 890 at 1kHz Capacitatnce density and dielectric loss were 47 fF/${\mu}{\textrm}{m}$2 and 0.47 respectively. As a result of measuring Curie temperature PFN thin films had Curie point with a rang of 110~12$0^{\circ}C$ and showed broad dielectric peak at that point. Leakage current of the PFN thin films were increased with increasing the annealing tempera-ture.

• Tribology and Lubricants
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• 제15권1호
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• pp.8-16
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• 1999

The electrorheological (ER) behavior of suspensions in silicone oil of phosphoric ester cellulose powder (average particle size : 18$\pm$1 ${\mu}{\textrm}{m}$) was investigated on the elevated temperature up to 10$0^{\circ}C$. For development of anhydrous ER fluids using at wide temperature range, it should be researched to how the effect of temperature on the ER activities. As a first step, the anhydrous ER suspensions mixing with the phosphoric ester cellulose particles which were made from the phosphoric ester reaction of cellulose were measured. As increasing the temperature, not only the analysis of electrical properties such as dielectric constant current density and electrical conductivity but also the rheological properties of ER fluids were studied. From the experimental results, the temperature had a large influence to the ER properties of anhydrous ER fluids. The current density, conductivity and elecoorheological effect ($\tau$$_{A}$$\tau$$_{0}$) of phosphoric ester cellulose ER fluids were proportional to the temperature with power law. And the shear stress of them was closely related with the square of dielectric constant mismatch parameter ($\beta$$^2$) under constant shear rate and electric field.d.

• 대한기계학회논문집
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• 제18권10호
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• pp.2585-2596
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• 1994

Many particle filled materials like Poweder/Binder mixtures for poweder injection moldings, have complicated rheological behaviors such as an yield stress and slip phenomena. In the present study, numerical simulation programs via a finite element method and a finite difference method were developed for the quasi-three-dimensional flows and the two-dimensional flow models, respectively, with the slip phenomena taken into account in terms of a slip velocity. In order to qualitatively understand the slip effects, typical numerical results such as vector plots, pressure contours in the cross-channel plane, and isovelocity controus for the down-channel direction were discussed with respect to various slip coefficients. Slip velocities along the boudary surfaces were also investigated to find the effects of the slip coefficient and processing conditions on the overall flow behavior. Based on extensive numerical calculations varying the slip coefficients, pressure gradient, aspect ratio, and power law index, the screw characteristics of the extrusion process were studied in particular with comparisons between the slip model and non-slip model.

• 펄프종이기술
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• 제46권3호
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• pp.1-10
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• 2014

Offset paper printing is a promising roll-to-roll technique for color printed materials. Although it is no doubt that understanding ink transfer mechanism in offset printing process is necessary to achieve high printing quality, investing the relationship between inks and substrates at the nip is difficult experimentally due to high printing speed. In this paper, rheological behavior and splitting point of the ink at the nip is studied using package software Ployflow and Flow 3D based on Navier-Stokes equation. Polydimethylsiloxane (PDMS) ink and IGT printability tester were used for an model ink and experiment to compare with that of simulation data, respectively. As a result, higher viscosity at state flow and pressure increased ink transfer due to higher possibility of presence of cavitation at the nip and increase in covering area ratio. These results have shown good agreements with experimental data compared by measuring density of print through.

• 유변학
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• 제9권1호
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• pp.6-15
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• 1997

계면활성제용액에 서로 다른 기능을 하는 두 종류의 첨가제를 투입하여 미셀의 미 세구조 전이현상을 규명하였다. 양이온 계면활성제는 CMC 이상의 농도에서 2단계의 미세 구조 전이거동을 나타낸다. 우선 구형 미셀은 첨가제의 투입에 의하여 표면에서의 친수성기 간의 반발력이 감소됨으로써 실린더형 또는 디스크형미셀로 전이가 일어난다. 더욱 농도가 증가하면 이방성을 가지는 실린더형 미셀간의 중첩 또는 hooking 현상에 의한 두 번째 전 이가 일어난다. 이때 미셀 용액은 흔히 점탄성을 나타내거나 확연한 비뉴톤성 유체거동을 나타낸다. 본 연구에선 heptanol의 화확구조적 차이가 물성에 나타내는효과를 규명하고 wormlike 미셀을 형성하는 MaSal에 의한 점탄성 거동을 살펴보았다. Heptanol의 화학구조 의 영향을 보면 약친수성기인 OH기가 알킬그룹과 나란하게 존재하여 밀집된 구조를 가지 기 쉬운 primary heptanol이 가장효과적으로 미세구조 전이를 유도함을 관찰하였다. 다른 이성질 hetanol의 경우 secondary heptanol이 teriary heptanol에 비하여 효과적임을 보이지 만 화학재할수 있는 농도범위가 매우 좁아 대부분 영역에서 비뉴톤성거동을 나타냄을 확인 하였다. 즉 NaSal를 사용한 경우 실린더형 미셀이 존재할 수 있는농도범위가 매우 좁아 대 부분 영역에서 비뉴톤성 거동을 나타냄을 확인하였다. 즉 NaSal 이 첨가된 용액은 선형점탄 성거동을 보이며 몰비가 증가함에 따라 scission 과정이 관찰되었다. 또한 몰농도비에 따라 항복응력과 shear thickening 특징을 보이는데 이는 흐름장의 세기에 따라 미세구조 변화가 일어나기 때문이다.

• Macromolecular Research
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• 제15권7호
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• pp.640-645
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• 2007

The phase behavior of branched polycarbonate (BPC) blends with poly(ethylene terephthalate-co-1,4-dimethyl cyclohexane terephthalate) copolyesters (PECT), as well as their rheological properties, were assessed. Even though BPC blends with PECT prepared by solvent casting proved to be immiscible, BPC and PECT copolyesters containing 1,4-dimethyl cyclohexane (CHDM) from 32 to 80 mole% formed homogeneous mixtures upon heating. The homogenization temperatures of the blends decreased with increasing CHDM content in PECT. The interaction energies of the BPC-PECT pairs calculated from the phase boundary in accordance with the lattice-fluid theory were positive and also decreased with increasing CHDM content in PECT. It was shown that the phase homogenization of these blends occurs upon heating when the combinatorial entropy term, which is favorable for miscibility, overcomes unfavorable energetic terms at elevated temperatures. A novel product, which is not limited by the drawbacks of linear polycarbonate (PC) and evidences processability superior to that of the PC/PECT blends, can be developed via the blending of BPC and PECT.

• Macromolecular Research
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• 제10권4호
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• pp.221-229
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• 2002

PET nanocomposites filled with fumed silicas were prepared via direct melt compounding method at various mixing conditions such as filler type and filler content. Some fumed silicas were pre-treated to improve the wettability and dispersibility, and principal characterizations were performed to investigate the effects of nano fumed silicas on polymer matrix. Hydrophobic fumed silica (M-FS), which has the similar contact angles of water with neat PET, acted as the best reinforcement for the thermal stability and mechanical properties of PET nanocomposite, and FE-SEM images also showed that M-FS was uniformly dispersed into matrix and had good wettability. But, some filler (O-FS) had low dispersibility and caused the deterioration of mechanical properties. Besides, the results of DSC revealed the nucleation effect of all fillers in polymer matrix, and PET nanocomposite filled with hydroptilic fumed silica (FS) showed markedly the characteristic dynamic rheological properties such as shear thinning behavior at very low frequencies and the decrease of viscosity.