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Humidity-dependent Electrical Conductance of Carbon/Polymer Composite Micro-Fibers
Hyung Jun Koo(구형준) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.2
Electrically conducting composites based on carbon nanomaterials, such as graphene and carbon nanotube, are under consideration for numerous applications, such as electronics, energy devices, and sensors. Here, I discuss dependence of electrical conductance of a carbon/agarose-based composite microfiber on environmental humidity. A simple and general process for fabrication of the composite microfiber has been developed, based on size reduction during dehydration of extruded composite hydrogel filaments. The resulting composite microfiber is robust and conducting enough for the fabrication of fiber-type microdevices. Its humidity-dependent conductance enables the composite fiber to be used as a humidity sensor with good sensitivity and fast response time. Interestingly, the dependency of electrical conductance of a composite fiber with the conducting nanofillers on humidity is significantly affected by filler content, which has been systematically investigated.
Interfacial Properties of Gallium-based Liquid Metal Alloys: Cytotoxicity and Wetting
Hyung Jun Koo(구형준) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.1
Due to their attractive properties, such as high electrical/thermal conductivity, fluidic characteristics, low surface energy and toxicity, numerous applications of the liquid metals have been developed in diverse fields ranging from stretchable/self-healing electrodes to thermal interfacing materials, and drug-delivery. The oxide nanolayer is naturally formed on the liquid metal, which significantly reduces the surface tension. Understanding of such an interfacial phenomenon is critical to manipulate the liquid metal having high surface tension (> 600 mNm<sup>-1</sup> in oxide-free state). In the first part of the talk, the cytotoxicity of the releasates from the surface of the liquid metal in water is discussed and compared to that of other toxic elements. In the second part of the talk, wetting characteristics of the liquid metal on various substrates with different materials and surface morphology is discussed.
Poly(2-hydroxyethyl methacrylate) 기반 공중합체 하이드로젤의 pH 의존 팽윤 거동 제어 연구
김수영(Sooyoung Kim),손승이(Seungyi Son),이종원(Jongwon Lee),구형준(Hyung-Jun Koo) 한국고분자학회 2019 폴리머 Vol.43 No.2
하이드로젤은 고도로 수화된 고분자 네트워크로서, 외부 자극에 따라 다른 팽윤 거동을 보이기 때문에 센서나 액츄에이터로 이용될 수 있다. 본 논문에서 우리는 poly(2-hydroxyethyl methacrylate)(PHEMA) 기반 공중합체의 pH 의존 팽윤 거동 제어 연구를 수행하였다. 먼저, 공중합체가 아닌 순수한 PHEMA는 매우 약한 pH 의존 팽윤 거동을 보임을 확인하였다. 이 PHEMA에 카복실기를 갖는 acrylic acid를 공중합할 경우, pH가 증가할수록 팽윤비가 크게 증가하였다. 이에 반해, PHEMA에 다이메틸아민기를 갖는 (2-dimethylamino)ethyl methacrylate)를 공중합할 경우, pH가 증가할수록 팽윤비가 감소하는 거동을 보였다. 이와 같이, 작용기를 적절하게 선택하여 PHEMA 고분자의 pH 의존 팽윤 거동 특성을 제어할 수 있다. 또한 더 큰 pH 의존 팽윤 거동 특성을 얻기 위해, PHEMA 중합시 개시제, 가교제 조성이 팽윤 거동에 미치는 영향에 대해 관찰하였다. 본 연구는 하이드로젤을 기반으로 한 센서나 액츄에이터와 같은 응용 분야에 유용한 정보를 제공할 수 있을 것이다. A hydrogel is a highly hydrated polymer network which can be used as a sensor and an actuator due to its different swelling behavior responsive to external stimuli. In this report, we discuss the pH-dependent swelling behavior of PHEMA-based copolymer hydrogels. The swelling behavior of the PHEMA homopolymer hydrogel has little pH dependency. However, when the PHEMA is copolymerized with acrylic acid, the copolymer swells more at high pH condition. When dimethyl amine functional groups are introduced to the PHEMA hydrogel, the copolymer shows the opposite swelling behavior, i.e. higher swelling ratio at lower pH condition. Thus, the swelling behavior of the PHEMA-based hydrogel can be controlled by introducing different functional groups. Furthermore, we investigate the effect of initiator and crosslinker compositions on the swelling ratio of the hydrogel, to achieve more drastic pH-dependent swelling behavior. This study would provide helpful information for hydrogel-based applications, such as sensors and actuators.