• Fibers and Polymers
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• v.4 no.3
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• pp.114-118
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• 2003

The prepolymer and the final polyurethane (PU) block copolymer were synthesized by reacting 4,4-methylene bis(phenylisocyanate) with poly(tetramethylene glycol) and the prepolymer with 1,4-butanediol as a chain extender, respectively, to investigate the relation between phase separation and it's resulting properties. According to FT-IR data, the phase separation of hard and soft segments in the prepolymer and the PU block copolymer grew bigger by increasing the hard segment content, and the PU showed more dominant phase separation than the prepolymer. The heat of fusion due to soft segments decreased in both the prepolymer and the PU by increasing the hard segment content, whereas the heat of fusion due to hard segments increased in the PU did not appear in the prepolymers. The breaking stress and modulus of the prepolymer increased by increasing the hard segment content, and the elongation at break decreased gradually, and the PU showed the highest breaking stress and modulus at 58% hard segment content. However, the best shape recovery of the PU was obtained at 47% hard segment content due to the existence of proper interaction among the hard segments for shape memory effect. Consequently, the mechanical properties and shape memory effect of the PU were influenced by the degree of phase separation, depending on the incorporation of chain extender as well as the hard segment content.

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.433-436
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• 2002

형상기억재료는 형상기억효과, 회복변형효과, 형상고청효과, 진동제어효과 등의 특성으로 인하여 중요한 지능재료(smart materials)의 하나로 기대되고 있다. 형상기억 재료로는 합금, 세라믹, 고분자, 겔 등을 들 수 있지만 Ti-Ni 합금(Nitinol)이 가장 많이 이용되고 있다. 그러나 형상기억고분자는 형상기억합금에 비하여 가볍고 형상회복률이 높으며 가공이 쉽고 투명할 뿐만 아니라 염색이 가능하기 때문에 물성과 경제적인 면에서 유리하다. (중략)

• Transactions of Materials Processing
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• v.22 no.4
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• pp.216-222
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• 2013

Solid polymers exhibit rate-dependent deformation behavior such as nonlinear strain rate sensitivity and stress relaxation like metallic materials. Despite the different microstructures of polymeric and metallic materials, they have common properties with respect to inelastic deformation. Unlike most metallic materials, solid polymers and shape memory alloys (SMAs) exhibit highly nonlinear stress-strain behavior upon unloading. The present work employs the viscoplasticity theory [K. Ho, 2011, Trans. Mater. Process. 20, 350-356] developed for the pseudoelastic behavior of SMAs, which is based on unified state variable theory for the rate-dependent inelastic deformation behavior of typical metallic materials, to depict the curved unloading behavior of polyphenylene oxide (PPO). The constitutive equations are characterized by the evolution laws of two state variables that are related to the elastic modulus and the back stress. The simulation results are compared with the experimental data obtained by Krempl and Khan [2003, Int. J. Plasticity 19, 1069-1095].

• Prospectives of Industrial Chemistry
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• v.24 no.6
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• pp.19-31
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• 2021

자극응답성 액정 엘라스토머(liquid crystal elastomer)는 하이드로겔(hydrogel), 형상 기억 고분자(shape memory polymer)와 더불어 생체 특성을 모방한 인공 근육, 소프트 액추에이터 및 소프트 로봇을 위한 스마트 소재로 최근 높은 관심을 받고 있다. 특히, 액정 엘라스토머는 고무 탄성과 액정 이방성이 결합된 비등방성 탄성 고분자로, 열, 빛, 전기 및 수분과 같은 외부자극에 반응하여 가역적이며, 액정 분자들의 배향조절을 통한 프로그램된 변형이 가능하다. 액정 엘라스토머가 개념 증명을 하는 수준을 넘어 실제로 유용한 소프트 액추에이터 및 로봇 시스템에 적용되기 위해서는 우수한 구동력 및 작업 용량, 높은 구동 변형률, 빠른 응답 시간, 낮은 구동 온도, 다양한 외부 자극반응성 및 높은 에너지 전환 효율 등을 확보하는 것이 중요하다. 본 기고문에서는 액정 엘라스토머의 개념에 대해 소개하고, 이러한 소재가 소프트 액추에이터로써 광범위하게 활용될 수 있도록 다양한 성능들을 향상시킬 수 있는 방법에 대해 소개하고자 한다.

• Fashion & Textile Research Journal
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• v.21 no.6
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• pp.697-707
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• 2019

This review paper deals with materials, classification, and a current article investigation on smart textile sensors for wearable vital signs monitoring (WVSM). Smart textile sensors can lose electrical conductivity during vital signs monitoring when applying them to clothing. Because they should have to endure severe conditions (bending, folding, and distortion) when wearing. Imparting electrical conductivity for application is a critical consideration when manufacturing smart textile sensors. Smart textile sensors fabricate by utilizing electro-conductive materials such as metals, allotrope of carbon, and intrinsically conductive polymers (ICPs). It classifies as performance level, fabric structure, intrinsic/extrinsic modification, and sensing mechanism. The classification of smart textile sensors by sensing mechanism includes pressure/force sensors, strain sensors, electrodes, optical sensors, biosensors, and temperature/humidity sensors. In the previous study, pressure/force sensors perform well despite the small capacitance changes of 1-2 pF. Strain sensors work reliably at 1 ㏀/cm or lower. Electrodes require an electrical resistance of less than 10 Ω/cm. Optical sensors using plastic optical fibers (POF) coupled with light sources need light in-coupling efficiency values that are over 40%. Biosensors can quantify by wicking rate and/or colorimetry as the reactivity between the bioreceptor and transducer. Temperature/humidity sensors require actuating triggers that show the flap opening of shape memory polymer or with a color-changing time of thermochromic pigment lower than 17 seconds.