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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>
Transparent and Flexible Photon Sieve Made with Cellulose Nanofiber by Micro-Nano Structure Molding
김현찬,Lindong Zhai,Pooja S. Panicker,김현정,David MacDonnell,김재환 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.9 No.4
Conventionally, the photon sieve (PS) was made of chrome-coated fused silica and quartz plates. However, fused silica and quartz plates have a size limitation due to their weight and fragility. A membrane PS is attractive since it is lightweight, large size, flexibility and deployable. This paper demonstrates the new concept of membrane PS based on cellulose nanofiber (CNF). The CNF-based PS (CNF-PS) is transparent, flexible, lightweight, and has high strength and toughness. This study highlights the PS fabrication on a CNF fi lm using a micro-nano structure molding technique and its structural stability in an external environmental change. For the first time in literature, through a high vacuum (5 × 10 –8 Torr) environment test, it was shown that CNF has emerged as a promising optical material. Furthermore, the prepared CNF-PS exhibited high beam quality. This study explained the complete research strategy from the isolation of cellulose nanofibers to its PS application. The new concept of CNF-PS will accelerate its broad application to thin and compact photonic devices.
Rheology Design and Experimental Test of Roll-to-Roll Process for Electroactive Cellulose Film
윤선진,Lindong Zhai,김현찬,김정웅,Ruth M. Muthoka,Debora Kim,김재환 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.9
This paper reports a theoretical model to analyze the roll-to-roll process for electroactive cellulose film that consists of casting, curing and drying processes, and the experimental data that reflect the effect of viscosity and rheology on the thickness control of the film. Analytical solutions were obtained from Navier-Stokes equation for the coupled fluid dynamic model reflecting the phase change of the cellulose during the curing and drying processes. The effect of the roll-to-roll casting speed on the flow velocity and the thickness of electroactive cellulose film were analyzed. The model successfully evaluated the flow velocity and the thickness of the processed films. Experimental verification on the analysis was conducted and the measured thickness data showed an inverse proportional relationship to the casting speed. Hole defects was observed during the fabrication of electroactive cellulose films, and the increased viscosity inside the blade gap and the lack of a yield stress in the fluid were presumed as the reasons for the hole defects. To remove the hole defects, dual ultrasonic vibration system was introduced. The results are applicable for roll-to-roll processes for other film fabrications.
Titanium Dioxide Sol-gel Schottky Diodes and Effect of Titanium Dioxide Nanoparticle
Maniruzzaman, Mohammad,Zhai, Lindong,Mun, Seongcheol,Kim, Jaehwan The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.6
This paper reports the effect of Titanium dioxide (TiO<sub>2</sub>) nanoparticles on a TiO<sub>2</sub> sol-gel Schottky diode. TiO<sub>2</sub> nanoparticles were blended with TiO<sub>2</sub> sol-gel to fabricate the Schottky diode. TiO<sub>2</sub> nanoparticles showed strong anatase and rutile X-ray diffraction peaks. However, the mixture of TiO<sub>2</sub> sol-gel and TiO<sub>2</sub> nanoparticles exhibited no anatase and rutile peaks. The forward current of the Schottky diode drastically increased as the concentration of TiO<sub>2</sub> nanoparticles increased up to 10 wt. % and decreased after that. The possible conduction mechanism is more likely space charge limited conduction.
Titanium Dioxide Sol-gel Schottky Diodes and Effect of Titanium Dioxide Nanoparticle
Mohammad Maniruzzaman,Lindong Zhai,Seongcheol Mun,Jaehwan Kim 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.6
This paper reports the effect of Titanium dioxide (TiO₂) nanoparticles on a TiO₂ sol-gel Schottky diode. TiO₂ nanoparticles were blended with TiO₂ sol-gel to fabricate the Schottky diode. TiO₂ nanoparticles showed strong anatase and rutile X-ray diffraction peaks. However, the mixture of TiO₂ sol-gel and TiO₂ nanoparticles exhibited no anatase and rutile peaks. The forward current of the Schottky diode drastically increased as the concentration of TiO₂ nanoparticles increased up to 10 wt. % and decreased after that. The possible conduction mechanism is more likely space charge limited conduction.
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>
Review of Soft Actuator Materials
김재환,김정웅,김현찬,Lindong Zhai,고현우,Ruth M. Muthoka 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.12
Soft actuator materials change their shape or size in response to stimuli like electricity, heat, light, chemical or pH. These actuator materials are compliant and well suited for soft mechatronics and robots. This paper introduces the definition of soft materials and the position of soft actuator materials in comparison with conventional actuators and other solid state actuator materials. A thorough review of selected soft actuator materials is carried out, including responsive gels/hydrogels, ionic polymer metal composites, conducting polymers, carbon nanotubues/graphenes, dielectric elastomers, shape memory polymers and biopolymers. This review will give insights for applications of soft actuator materials via better understanding of the materials in terms of their preparation, performance and limitation.
Akther, Asma,Kafy, Abdullahil,Zhai, Lindong,Kim, Hyun Chan,Shishir, MD Imrul Reza,Kim, Jaehwan IOP 2016 Smart materials & structures Vol.25 No.11
<P>This study deals with ultrasonic wave propagation on a piezoelectric polymer substrate for tactile actuator. On the piezoelectric polymer substrate, a pair of interdigital transductor (IDT) electrodes is patterned by lift-off process and a resonator is made by exciting the IDTs. A standing wave is generated between the pair of IDT electrodes, of which the wavelength matches with the distance between two IDTs. The standing ultrasonic waves can give different textures to the users. The wave propagation in this periodic structure on the polymer substrate is studied by harmonic and transient analysis. Vertical displacement and induced voltage at the output IDT electrode are calculated and the ultrasonic wave generation is experimentally verified. The proposed concept of tactile actuator based on ultrasonic wave is explained.</P>