• Macromolecular Research
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• 제17권3호
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• pp.156-162
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• 2009

Supramolecular hydrogels were instantaneously fabricated by mixing aqueous solutions of $\alpha$-cyclodextrins ($\alpha$-CDs) and amphiphilic methoxy (polyethylene glycol) (MPEG)-$\varepsilon$-caprolactone (CL) oligomer, which was synthesized via the ring-opening polymerization of the CL monomer using low-molecular-weight MPEG ($M_n$ of MPEG=2,000 g/mol) as an initiator. The supramolecular structure of the hydrogels was revealed by X-ray diffraction (XRD) analyses. Rheological studies of the hydrogels revealed an elastic character when the number of CL units in the oligomer was more than 2, and the obtained hydrogels showed high storage modulus but relatively low shearing viscosity due to the low-molecular-weight character of the oligomer, which was more preferable for use as an injectable delivery system. The physical properties of the hydrogels could be modulated by controlling the chain morphology and concentration of the oligomers, as well as the feed molar ratio of the oligomer to $\alpha$-CD. The components of the supramolecular hydrogels are biocompatible and can readily be eliminated from the body. These features render the supramolecular hydro gels suitable as drug delivery systems and tissue engineering scaffolds.

• Geomechanics and Engineering
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• 제23권6호
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• pp.535-546
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• 2020

The stress environment of deep rock masses is complex. Under the action of earthquakes or blasting, the strength and stability of anchored rock masses in fracture zones or faults are affected. To explore the variation in anchored rock masses under creep-fatigue loading, shear creep comparative testing of anchored marble specimens with or without fatigue loading is performed. Considering the damage variable of rock under fatigue loading, a rheological model is established to characterize the whole shear creep process of anchored rock masses under creep-fatigue loading. The results show that (1) the overall deformation of marble under creep-fatigue loading is larger than that under only shear creep loading, and the average deformation is increased by 18.3%. (2) By comparing the creep curves with and without fatigue loading, the two curves basically coincide when the first level stress is applied, and the two curves are stable with the increase in stress level. The results show that the strain difference among the specimens increases gradually in the steady-state stage and reaches the maximum at the fourth level. (3) The shear creep is described by considering the creep mechanical properties of anchored rock masses under fatigue loading. The accuracy of this creep-fatigue model is verified by laboratory tests, and the applicability of the model is illustrated by the fitting parameter R2. The proposed model provides a theoretical basis for the study of anchored rock masses under low-frequency earthquakes or blasting and new methods for the stability and reinforcement of rock masses.

• Advances in nano research
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• 제13권1호
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• pp.13-28
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• 2022

The pumpability of the grouts is significant issue in concept of the rheological and workability properties during penetrating to voids and cracks. To improve the fluidity features of the grout mixes, the usage of Colloidal Nano Particular Powders (CNPPs) with mineral additives such as fly ash (FA) can contribute. Therefore, the main purpose of this study can be explained as investigating the usage effects of four types of Colloidal Nano Particular Powders (n-TiO₂, n-ZnO, n-Al₂O₃ and n-SiO₂) as nano additives on the rheological, workability and bleeding properties of cement-based grout incorporated with fly as. Test results showed that the usage of FA in the grout samples positively contribute to increase on the fluidity of the grout samples as expected. The dilatant behavior was observed from the results for all mixes. Observing the effect of nano-sized additives in such cement-based grout mixtures with high fluidity has presented remarkable effects in this study.

• Composites Research
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• 제19권3호
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• pp.15-22
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• 2006

유리섬유로 강화된 폴리프로필렌 복합재료를 이축압출장치를 이용하여 제조하였으며 폴리프로필렌 수지와 유리섬유간의 결합성을 증대시키고 가공성을 향상시킬 목적으로 말레익 안하이드라이드(maleic anhydride) 결합기를 가지는 상용화제를 첨가하였다. 제조된 폴리프로필렌/유리섬유 복합재료에 대한 전단유동과 신장유동의 특성을 조사하였으며, 특히 상용화제 첨가와 유리섬유의 함량에 대한 영향을 주로 평가하였다. 전단유동에서 상용화제는 폴리프로필렌과 유리섬유간의 결합력을 증대시키고, 흐름성을 개선시키는 역할을 하였으며, 신장유동에서는 유리섬유의 함량이 증가됨에 따라서 신장점도를 더욱 증가시켜주는 역할을 하였다. 그러나 신장속도가 증가함에 따라서 유리섬유 사이에서 형성되는 미세한 전단유동의 영향으로 오히려 신장점도는 감소하였다.

• Elastomers and Composites
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• 제41권2호
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• pp.97-107
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• 2006

폐타이어와 폐수지 처리 문제를 해결하기 위한 방법으로 재생 폴리에틸렌 수지와 신재HDPE를 폐타이어 분말(GWTP)과 치합형 동방향 회전 이축 압출기(Fuly Intermeshing Co-rotating Twin Screw Extruder)를 이용하여 각 조성별로 용융 훈련하여 재생 PE/폐타이어 복합체를 제조하였다. 본 연구에서는 플라스틱 수지 (재생 PE, HDPE)와 폐타이어 분말의 혼합비를 $0\sim50$wt.%로 하였으며, ASTM에 의거하여 인장강도, 파단신율, 충격강도 등의 물성 변화를 확인하였다. 폐타이어 분말 함량이 증가할수록 인장강도가 감소하고 파단신율이 증가하였다. 한편 충격강도는 폐타이어 분말 함량이 30 wt.%일 때 최대이고, 함량이 증가할수록 충격 강도가 감소하는 경향을 나타내었다. 형태학적 고찰에서는 폐타이어 분말의 함량의 증가함에 따라 파단면이 거칠어지는 형상을 관찰하였다. 모세관점도계(Capillary Rheometer)를 이용하여 재생 PE/폐타이어 분말 복합체의 전단속도의 변화에 따른 용융전단점도의 변화와 연화점 (Ts) 등의 유변학적 성질을 분석한 결과, 폐타이어 분말 함량 증가에 따라 외부 응력에 대한 흐름 저항성을 증가시켜 용융점도가 상승하는 결과를 보였으며 측정된 전단율에서 전단 점도는 Power-law 거동을 보였다.

• Fibers and Polymers
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• 제2권3호
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• pp.129-134
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• 2001

Liquid crystalline (LC) poly(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate) (50/50, mole/mole) [PECPT] was synthesized and blended with polycarbonate (PC). LC properties of PECPT and thermal, morphological, and rheological behaviors of the PECPT/PC blend were studied. PECPT showed the nematic LC phase and much longer relaxation time than poly(ethylene terephthalate) (PET). The apparent melt viscosity of PECPT was one third of that of FET. An abrupt torque change was observed during the blending process due to the orientation of LC domains. For the blends containing 10~30 wt% of PECPT, the complex viscosities were higher than that of PC. As PECPT content increases above 40 wt%, shear thinning was observed. The lowest complex viscosity was obtained at 40~50 wt%. Transesterification of PECPT and PC was confirmed by the selective chemical degradation of carbonate groups in PC.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.41-44
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• 1997

Dispersion and flocculation behaviors of clay-ash powders in a slurry state were examined, and we have systematically investigated the effects of colloid/interfaces variables on slip properties and the rheological behavior of ash-clay slurry. Ash-clay slurries have been characterized on the basis of the time dependent rheology which was done out by the gel-curve test. Gel-curve for the coagulated slip shows interesting rheological behavior which was caused by the formation of the new network structure and the readsoption of the polysilicon hydroxo species on the particle surfaces.

• 소성∙가공
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• 제14권4호
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• pp.338-350
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• 2005

Recently, in the field of automobile industry, to solve the problem of reducing the weight of automobile for the improvement of fuel efficiency and the protection of environment, the aluminum alloy parts have been substituted for the steel parts. However, the aluminum alloy does not have as good mechanical property as the steel part. To improve the mechanical property, the semi-solid die casting process is performed to make automobile parts. In the fabrication of semisolid material the control of the liquid segregation is very important to improve the material properties of aluminum alloy. In the present paper we examine the influence of the liquid segregation by the injection conditions in the semi-solid die casting has been investigated.

• Korea-Australia Rheology Journal
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• 제21권2호
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• pp.103-108
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• 2009

Hemorheological properties are easily modified by glucose-induced oxidation and glycation. Carnosine, a naturally occurring dipeptide ($\beta$-alanyl-LFull-size image-histidine), has been recently proposed to act as an antioxidant as well as a free-radical scavenger. In the present study, we investigate its protective and rejuvenating effects in erythrocytes that are exposed to glucose-rich plasma. Erythrocytes that were incubated in glucose solutions were treated with different concentrations of carnosine and for different incubation times. Their hemorheological alterations were examined. The results reveal that the presence of carnosine effectively prevented these rheological alterations in a concentration-dependent manner in glucose-rich media. It is proposed that moderate concentrations of carnosine might be further explored as potential therapeutic agents for pathologies that involve hemorheological modification.

• 한국식품저장유통학회지
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• 제4권3호
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• pp.343-349
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• 1997

The rheological Voperties of biopolymers produced by Bacilli sp. K-1 and its mutant strains(KM-21, KM-83) were studied at the temperature ranges with 20∼80$^{\circ}C$, at the concenration of 2∼6%, at the pH ranges from 3.0 to 9.0 and at the shear rate of 9.3-930sec-1 The apparent viscosity of biopolymers was decreased with increasing shear rate, and thereby biopolymers showed pseudoplastic characteristics. It was found that the apparent viscosity models respected 19 temperature, concentration and both temperature and concentration were expressed by Arrhenius Model, Exponential Model and combined of the above two Models. Therefore, the apparent viscosity could be predictable by Arrhenius and Exponential Models with high R2.