Seongcheol Mun

Disposable chemical sensors and biosensors made on cellulose paper

Most sensors are based on ceramic or semiconducting substrates, which have no flexibility or biocompatibility. Polymer-based sensors have been the subject of much attention due to their ability to collect molecules on their sensing surface with flexibility. Beyond polymer-based sensors, the recent discovery of cellulose as a smart material paved the way to the use of cellulose paper as a potential candidate for mechanical as well as electronic applications such as actuators and sensors. Several different paper-based sensors have been investigated and suggested. In this paper, we review the potential of cellulose materials for paper-based application devices, and suggest their feasibility for chemical and biosensor applications.

Transparent and Flexible Cellulose Nanocrystal/Reduced Graphene Oxide Film for Proximity Sensing

The rapid development of touch screens as well as photoelectric sensors has stimulated the fabrication of reliable, convenient, and human-friendly devices. Other than sensors that detect physical touch or are based on pressure sensing, proximity sensors offer controlled sensibility without physical contact. In this work we present a transparent and eco-friendly sensor made through layer-by-layer spraying of modified graphene oxide filled cellulose nanocrystals on lithographic patterns of interdigitated electrodes on polymer substrates, which help to realize the precise location of approaching objects. Stable and reproducible signals generated by keeping the finger in close proximity to the sensor can be controlled by humidity, temperature, and the distance and number of sprayed layers. The chemical modification and reduction of the graphene oxide/cellulose crystal composite and its excellent nanostructure enable the development of proximity sensors with faster response and higher sensitivity, the integration of which resolves nearly all of the technological issues imposed on optoelectronic sensing devices.

Fabrication of Cellulose ZnO Hybrid Nanocomposite and Its Strain Sensing Behavior

This paper reports a hybrid nanocomposite of well-aligned zinc oxide (ZnO) nanorods on cellulose and its strain sensing behavior. ZnO nanorods are chemically grown on a cellulose film by using a hydrothermal process, termed as cellulose ZnO hybrid nanocomposite (CEZOHN). CEZOHN is made by seeding and growing of ZnO on the cellulose and its structural properties are investigated. The well-aligned ZnO nanorods in conjunction with the cellulose film shows enhancement of its electromechanical property. Strain sensing behaviors of the nanocomposite are tested in bending and longitudinal stretching modes and the CEZOHN strain sensors exhibit linear responses.

Synthesis and characterization of iron oxide/cellulose nanocomposite film.

Iron oxide/cellulose high-performance nanocomposite film is successfully prepared by impregnation of iron oxide nanoparticles into a regenerated cellulose film. The structure, thermal stability and mechanical properties of the nanocomposite films are investigated by the wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mechanical pull test. The investigation results reveal that the iron oxide is bound to hydroxyl groups of the regenerated cellulose film by hydrogen bonding. Compared with the regenerated cellulose, the tensile strength and elastic modulus of iron oxide/cellulose high-performance films are significantly improved by about 39% and 57%, respectively.

Flexible cellulose acetate/graphene blueprints for vibrotactile actuator

Tactile devices containing many actuators within are being sutured using electroactive polymers. This innovation forms the basis of hand-like tactile feedback in emerging smart robotic manipulation. Here, we introduce low power consuming modified reduced graphene oxide embedded cellulose acetate composite of high flexibility and conformability to surfaces made by simple and low cost synthesis methods, which thus points towards simple read-out electronics. The material performance was evaluated based on various actuation conditions in terms of electrical potential, bias voltage, temperature and frequency. The actuator vibrating at various frequencies with faster response time illustrates a range of haptic feedbacks to users, which can be used in braille display devices. Excellent repeatability of the haptic actuation process was also noticed.

Flexible and transparent strain sensor made with silver nanowire–coated cellulose

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 0.01 wt% silver nanowire is coated on the cellulose film, 70% transmittance is maintained with 2.4 kΩ/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.

Preparation and characterization of Cellulose-ZnO nanolayer film by blending method

Cellulose-ZnO nanolayer film (CZNF) was prepared by simply mixing ZnO nanopowder with cellulose solution and sodium dodecyl sulphate dispersing agent. CZNF was cured in a mixture of isopropyl alcohol and deionized water and a freestanding film was obtained. CZNF was prepared with different weight percentage of ZnO and all materials were characterized by optical, thermal, mechanical and electrical methods. The morphology shows that ZnO nanoparticles are evenly dispersed between cellulose nanolayers of CZNF. Thermal and mechanical test results exhibit that CZNF possesses two distinctive characteristics of regenerated cellulose and ZnO. Its complex electrical impedance exhibits very similar to ionic membranes for fuel cells.

Cellulose based soft gel like actuator for reconfigurable lens array

Reconfigurable lens is biomimetic as it mimics human eye and is a transparent actuating material that can change its curvature in the presence of external stimuli. Focus tunable, adaptive lenses provide several advantages over traditional lens assemblies in terms of compactness, cost, efficiency and flexibility. To further improve the simplicity and compact nature of adaptive lenses, we present lens system which makes use of an inline, transparent electro active polymer actuator. This paper reports the preliminary development we have achieved in reconfigurable lens systems made with cellulose nanocrystals (CNC) using the principle of Kerr effect. Preparation of the hydrophobic CNC solution as well as the optical properties of the lens has been discussed. This soft gel actuator was analyzed by measuring the electric birefringence in the pulse field of constant and sinusoidal voltage based on the use of modulation of elliptic light polarization.

Flexible cellulose and ZnO hybrid nanocomposite and its UV sensing characteristics

Abstract 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.

Cellulose electro-active paper fabricated by facile solvent exchange pretreatment and its physical and electromechanical properties

AbstractThe 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.