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Flexible and transparent strain sensor made with silver nanowire–coated cellulose
Mun, Seongcheol,Zhai, Lindong,Min, Seung-Ki,Yun, Youngmin,Kim, Jaehwan SAGE Publications 2016 Journal of intelligent material systems and struct Vol.27 No.8
<P>Simple and versatile method of layer-by-layer deposition is used to coat silver nanowire on a cellulose film to fabricate a flexible and transparent strain sensor. Strain-sensing behaviors of such a simply fabricated cellulose film are analyzed in both stretching and bending modes. When 0.01wt% silver nanowire is coated on the cellulose film, 70% transmittance is maintained with 2.4 k Omega/sq of sheet resistance, which is applicable for transparent electrode of the strain sensor. Conductivity of the transparent electrode is maintained after mechanical stretching, which demonstrates that the silver nanowire coating is securely adhered on the surface of cellulose film. The strain sensor shows high strain sensitivity and good gauge factor maintaining good transparency at low silver nanowire concentration, which might be associated with the tunneling resistance change in the silver nanowire. The morphology of the silver nanowire-coated cellulose strain sensor is investigated using an atomic force microscopy with an increase in silver nanowire concentration.</P>
Mun, Seongcheol,Yun, Sungryul,Jung, Hyejun,Kim, Jaehwan Elsevier 2012 Current Applied Physics Vol.12 No.suppl1
<P><B>Abstract</B></P><P>This paper reports sintering condition effect on an ink-jet printed conductive pattern of silver ink made on a cellulose paper. To fabricate the conductive pattern on the cellulose paper, silver ink is ink-jet printed and the influence of sintering temperature and time is investigated in terms of electrical resistivity and morphology by using scanning electron microscope and atomic force microscope. Two-level baking process composed of soft baking and hard baking is found to be effective for silver nanoparticle network. The sintering temperature and time are strongly associated with the conductivity of the ink-jet printed pattern.</P>
Electro-Active Polymer Based Soft Tactile Interface for Wearable Devices
Mun, Seongcheol,Yun, Sungryul,Nam, Saekwang,Park, Seung Koo,Park, Suntak,Park, Bong Je,Lim, Jeong Mook,Kyung, Ki-Uk IEEE 2018 IEEE transactions on haptics Vol.11 No.1
<P>This paper reports soft actuator based tactile stimulation interfaces applicable to wearable devices. The soft actuator is prepared by multi-layered accumulation of thin electro-active polymer (EAP) films. The multi-layered actuator is designed to produce electrically-induced convex protrusive deformation, which can be dynamically programmable for wide range of tactile stimuli. The maximum vertical protrusion is <TEX>${{650}}\,\mu {\mathrm{m}}$</TEX><alternatives> </alternatives> and the output force is up to 255 mN. The soft actuators are embedded into the fingertip part of a glove and front part of a forearm band, respectively. We have conducted two kinds of experiments with 15 subjects. Perceived magnitudes of actuator's protrusion and vibrotactile intensity were measured with frequency of 1 Hz and 191 Hz, respectively. Analysis of the user tests shows participants perceive variation of protrusion height at the finger pad and modulation of vibration intensity through the proposed soft actuator based tactile interface.</P>
Flexible cellulose and ZnO hybrid nanocomposite and its UV sensing characteristics
Mun, Seongcheol,Kim, Hyun Chan,Ko, Hyun-U,Zhai, Lindong,Kim, Jung Woong,Kim, Jaehwan unknown 2017 SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Vol.18 No.1
<P><B>Abstract</B></P><P>This paper reports the synthesis and UV sensing characteristics of a cellulose and ZnO hybrid nanocomposite (CEZOHN) prepared by exploiting the synergetic effects of ZnO functionality and the renewability of cellulose. Vertically aligned ZnO nanorods were grown well on a flexible cellulose film by direct ZnO seeding and hydrothermal growing processes. The ZnO nanorods have the wurtzite structure and an aspect ratio of 9 ~ 11. Photoresponse of the prepared CEZOHN was evaluated by measuring photocurrent under UV illumination. CEZOHN shows bi-directional, linear and fast photoresponse as a function of UV intensity. Electrode materials, light sources, repeatability, durability and flexibility of the prepared CEZOHN were tested and the photocurrent generation mechanism is discussed. The silver nanowire coating used for electrodes on CEZOHN is compatible with a transparent UV sensor. The prepared CEZOHN is flexible, transparent and biocompatible, and hence can be used for flexible and wearable UV sensors.</P>
Zhai, Lindong,Mun, Seongcheol,Gao, Xiaoyuan,Kim, Jeong Woong,Kim, Jaehwan Springer-Verlag 2015 Cellulose Vol.22 No.2
<P>The cellulose electro-active paper (EAPap) has been discovered as a smart material that can be used for sensors, actuators and flexible electronics. EAPap is made from regenerated cellulose that requires dissolving cellulose pulp using solvents with a heating process. However the heating process in dissolving cellulose is very critical to the performance of EAPap. In this paper, we introduce a new fabrication process of cellulose EAPap with a pretreatment process of cellulose, which simplifies the fabrication process and does not require the heating process. The pretreatment process includes the first immersion of cellulose into deionized water and the second immersion it into N,N-dimethylacetamide (DMAc) solvent, followed by twice repeat of the immersions. The pretreated cellulose was dissolved using lithium chloride (LiCl)/DMAc solvent without heating, which gives a cellulose solution. The pretreated cellulose solution was compared with another cellulose solution made with the LiCl/DMAc solvent and a heating process in terms of viscosity and solubility. Cellulose EAPap samples were made by using two cellulose solutions and their physical and electromechanical properties were compared in terms of transparency, ion concentration, surface morphology, Young's modulus, dielectric constant and piezoelectric charge constant. The pretreatment of cellulose results in similar or better physical properties of EAPap, which simplifies the cellulose EAPap fabrication.</P>
Kim, Hyun Chan,Mun, Seongcheol,Ko, Hyun-U,Zhai, Lindong,Kafy, Abdullahil,Kim, Jaehwan IOP 2016 Smart materials & structures Vol.25 No.7
<P>The use of renewable materials is essential in future technologies to harmonize with our living environment. Renewable materials can maintain our resources from the environment so as to overcome degradation of natural environmental services and diminished productivity. This paper reviews recent advancement of renewable materials for smart material applications, including wood, cellulose, chitin, lignin, and their sensors, actuators and energy storage applications. To further improve functionality of renewable materials, hybrid composites of inorganic functional materials are introduced by incorporating carbon nanotubes, titanium dioxide and tin oxide conducting polymers and ionic liquids. Since renewable materials have many advantages of biocompatible, sustainable, biodegradable, high mechanical strength and versatile modification behaviors, more research efforts need to be focused on the development of renewable smart materials.</P>