Gyu-Young Yun

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.

Paper transistor made with covalently bonded multiwalled carbon nanotube and cellulose

We report a flexible paper transistor made with regenerated cellulose and covalently bonded multiwalled carbon nanotube (RC-MWCNT). MWCNT bonded to cellulose chains can act as electron channel paths in dielectric cellulose layers. It is found that the covalent bonding between cellulose and MWCNT can be modulated by reaction time and temperature. The RC-MWCNT paper transistor shows that the leakage current and the on/off ratio are strongly associated with the concentration of MWCNTs. The estimated electron mobility of RC-MWCNT paper is comparable to other organic transistor materials. The RC-MWCNT paper transistor has a potential for flexible electronic paper.

Electrically aligned cellulose film for electro-active paper and its piezoelectricity

Electrically aligned regenerated cellulose films were fabricated and the effect of applied electric field was investigated for the piezoelectricity of electro-active paper (EAPap). The EAPap was fabricated by coating gold electrodes on both sides of regenerated cellulose film. The cellulose film was prepared by dissolving cotton pulp in LiCl/N,N-dimethylacetamide solution followed by a cellulose chain regeneration process. During the regeneration process an external electric field was applied in the direction of mechanical stretching. Alignment of cellulose fiber chains was investigated as a function of applied electric field. The material characteristics of the cellulose films were analyzed by using an x-ray diffractometer, a field emission scanning electron microscope and a high voltage electron microscope. The application of external electric fields was found to induce formation of nanofibers in the cellulose, resulting in an increase in the crystallinity index (CI) values. It was also found that samples with higher CI values showed higher in-plane piezoelectric constant, d31, values. The piezoelectricity of the current EAPap films was measured to be equivalent or better than that of ordinary PVDF films. Therefore, an external electric field applied to a cellulose film along with a mechanical stretching during the regeneration process can enhance the piezoelectricity.

Dielectric and polarization behaviour of cellulose electro-active paper (EAPap)

Dielectric and polarization behaviour of electro-active paper (EAPap) were studied to understand the detailed material behaviour of EAPap as a novel smart material. It was revealed that the dielectric constant of EAPap was temperature and frequency dependent. The largest change in the dielectric constant was observed near 0 ◦ C while the highest dielectric constant was obtained at around 100 ◦ C, which might be related to the dipolar behaviour of the hydroxyl structure of cellulose and adsorbed or existing internal water molecules in cellulose EAPap. By thermal stimulated current measurement for polarization behaviour of cellulose EAPap, it was shown that the maximum current was observed in the temperature range 105-110 ◦ C. Compared with the polarization behaviour in the low temperature range, abnormal polarization was observed under an applied field mainly due to the trapped space charge in EAPap, which indicates that cellulose EAPap has a similar material behaviour to that of electret polymers. (Some figures in this article are in colour only in the electronic version)

An electro-active paper actuator made with lithium chloride/cellulose films: effects of glycerol content and film thickness

Cellulose-based electro-active paper (EAPap) has been reported as a smart material that has merits in terms of light weight, dry condition, biodegradability, large displacement output and low actuation voltage. However, it requires high humidity. This paper introduces an EAPap that can be actuated in low humidity conditions. The fabrication process and performance test of the EAPap actuator are illustrated. Cellulose fibers were dissolved in N,N-dimethylacetamide/lithium chloride. The solution was cast and immersed in water to form the cellulose film, followed by adding glycerol and lithium chloride aqueous solution, and drying in air. Depositing thin gold electrodes on both sides of the cellulose film made a bending EAPap actuator. Effects and optimum values of the glycerol content and the thickness of the films are discussed.

Film-type haptic actuator made with cellulose acetate layers

We report a film-type haptic actuator made with two cellulose acetate active membranes and an air gap. Two different configurations of the actuators, double cellulose acetate membranes and single cellulose acetate membrane, are investigated. Due to the intensified electrostatic attraction force between chargeable cellulose acetate membranes, the double cellulose acetate membrane case shows over 300% displacement enhancement. Under a bias electric field, the displacement can be 200% improved comparing with no bias case. When the actuator performance of the cellulose acetate membrane is compared with polyethylene terephthalate and polyvinyl chloride membranes, the cellulose acetate membrane shows superior displacement output due to its high dielectric property. The cellulose acetate double membrane actuator has a great potential as kinesthetic actuator of haptic devices.

Cellulose electro-active paper: actuator, sensor and beyond

Recently, cellulose has been discovered as a smart material that can be used as sensors and actuators. This newly discovered material is termed as electro-active paper (EAPap) that has merits in terms of lightweight, flexible, dryness, biodegradable, biocompatible, easy to chemically modify, cheap and abundance. The actuation principle of cellulose EAPap bending actuator is known to be a combination of piezoelectric effect and ion migration effect. This paper presents further investigation of cellulose EAPap for its possibilities in biomimetic actuator, sensor, MEMS, acoustic devices and others. Biomimetic actuator is made with cellulose EAPap by fabricating rectifying antenna (rectenna) array on it. Cellulose EAPap material is customized to satisfy the material requirement for actuators and other devices. The material improvement all about cellulose EAPap is introduced. To fabricate the rectenna array, micro patterning of metallic layer in conjunction with Schottky diode fabrication on the cellulose was made. The Schottky diode fabrication allows possibility of thin film transistor fabricated on a cellulose paper. Microwave power transmission is demonstrated by using rectenna arrays, which can be used for many applications. Some of the device fabrication along with brief demonstrations is illustrated.

Haptic device development based on electro static force of cellulose electro active paper

Haptic is one of well-considered device which is suitable for demanding virtual reality applications such as medical equipment, mobile devices, the online marketing and so on. Nowadays, many of concepts for haptic devices have been suggested to meet the demand of industries. Cellulose has received much attention as an emerging smart material, named as electro-active paper (EAPap). The EAPap is attractive for mobile haptic devices due to its unique characteristics in terms of low actuation power, suitability for thin devices and transparency. In this paper, we suggest a new concept of haptic actuator with the use of cellulose EAPap. Its performance is evaluated depending on various actuation conditions. As a result, cellulose electrostatic force actuator shows a large output displacement and fast response, which is suitable for mobile haptic devices.

Hybrid nanocomposites made with cellulose and ZnO nanoparticles and its biosensing application

This paper reports a flexible and disposable ZnO blended cellulose hybrid nanocomposites (Cellulose/ZnO hybrid) film and its feasibility for a resistive glucose biosensor. Cellulose/ZnO hybrid film was fabricated by simply blending ZnO nanoparticles with cellulose solution prepared by dissolving cotton pulp with LiCl/DMAc solvent. Cellulose/ZnO hybrid film was cured in isopropyl alcohol and water mixture and free standing film was obtained. For biosensor application, the enzyme glucose oxidase was immobilized into the Cellulose/ZnO hybrid film by physical adsorption method. The enzyme activity of the glucose biosensor increases as the ZnO weight ratio increases linearly in the range of 1-12mM.

Piezoelectric paper speaker using a regenerated cellulose film

Acoustic performance of regenerated cellulose electroactive paper (EAPap) as a thin flexible film speaker was investigated. The enhancement of piezoelectric properties was obtained by a simple mechanical stretching process. As a prototype of flexible paper speaker, the sound pressure level (SPL) of cellulose EAPap film was evaluated as a function of distance, speaker size and geometry. It was revealed that the higher acoustic output from a small rectangular shape in low frequency range, while circular one seems to be better than that of all rectangular type speakers in audible frequencies.