Suresha K. Mahadeva

Paper Actuators Made with Cellulose and Hybrid Materials

Recently, cellulose has been re-discovered as a smart material that can be used as sensor and actuator materials, which is termed electro-active paper (EAPap). This paper reports recent advances in paper actuators made with cellulose and hybrid materials such as multi-walled carbon nanotubes, conducting polymers and ionic liquids. Two distinct actuator principles in EAPap actuators are demonstrated: piezoelectric effect and ion migration effect in cellulose. Piezoelectricity of cellulose EAPap is quite comparable with other piezoelectric polymers. But, it is biodegradable, biocompatible, mechanically strong and thermally stable. To enhance ion migration effect in the cellulose, polypyrrole conducting polymer and ionic liquids were nanocoated on the cellulose film. This hybrid cellulose EAPap nanocomposite exhibits durable bending actuation in an ambient humidity and temperature condition. Fabrication, characteristics and performance of the cellulose EAPap and its hybrid EAPap materials are illustrated. Also, its possibility for remotely microwave-driven paper actuator is demonstrated.

Effect of Room Temperature Ionic Liquids Adsorption on Electromechanical Behavior of Cellulose Electro-Active Paper

The cellulose smart material called electro-active paper (EAPap) is made by regenerating cellulose. However, the actuator performance is degraded at low humidity levels. To solve this drawback, EAPap bending actuators were made by activating wet cellulose films in three different room-temperature ionic liquids: 1-butyl-3-methylimidazolium hexaflurophosphate (BMIPF6), 1-butyl-3-methylimidazolium chloride (BMICL) and 1-butyl-3-methylimidazolium tetrafluroborate (BMIBF4). In the results, the actuator performance was dependent on the type of anions in the ionic liquids, in the order of BF4> Cl > PF6. The BMIBF4-activated actuator showed the maximum displacement of 3.8 mm with low electrical power consumption at relatively low humidity. However, the BMICL-activated actuator showed a slight degradation of actuator performance. Further performance and durability improvement will be possible once various ionic liquids are blended with cellulose.

Nanocoating of ionic liquid and polypyrrole for durable electro-active paper actuators working under ambient conditions

This paper reports that nanocoating of polypyrrole (PPy) and ionic liquid (IL) on cellulose film improves the electromechanical performance and durability of a cellulose electro-active paper actuator. Cellulose–PPy–IL nanocomposites were fabricated by the polymerization-induced adsorption process of PPy followed by subsequent activation in IL solutions. X-ray photoelectron spectroscopy, transmission electron microscopy and secondary ion mass spectroscopy analyses validated the successful nanocoating of the PPy and IL layers on the cellulose. The results revealed that the cellulose–PPy–IL nanocomposites are suitable for durable bending actuators working under ambient conditions. Preparation, characterization and performance test of the nanocomposites are explained.

The preparation, characterization and actuation behavior of polyaniline and cellulose blended electro-active paper

This paper reports polyaniline and cellulose blended electro-active paper (EAPap) that can produce large bending displacement at ambient humidity conditions with long lifetime durability. A novel solution processable polyaniline-p-toluene sulfonate (PANI–PTSA) salt was prepared by an inverted emulsion polymerization technique using benzoyl peroxide and p-toluene sulfonic acid. Cellulose solution prepared by dissolving cotton with lithium chloride/N, N-dimethylacetamide was mixed with the PANI emaraldine salt solution and a cellulose–PANI blended film was obtained. The obtained cellulose–PANI film was characterized by ultraviolet–visible (UV–visible), x-ray diffraction, scanning electron microscopy and tensile test methods. A cellulose–PANI EAPap actuator was made by depositing very thin gold electrodes on both sides of the cellulose–PANI film. When the actuator performance of the cellulose–PANI EAPap was evaluated in terms of bending displacement with respect to the actuation frequencies, voltages and relative humidity levels, a large bending displacement was shown at ambient humidity conditions with long lifetime durability.

Hybrid nanocomposite based on cellulose and tin oxide: growth, structure, tensile and electrical characteristics

Abstract A highly flexible nanocomposite was developed by coating a regenerated cellulose film with a thin layer of tin oxide (SnO2) by liquid-phase deposition. Tin oxide was crystallized in solution and formed nanocrystal coatings on regenerated cellulose. The nanocrystalline layers did not exfoliate from cellulose. Transmission electron microscopy and energy dispersive x-ray spectroscopy suggest that SnO2 was not only deposited over the cellulose surface, but also nucleated and grew inside the cellulose film. Current–voltage characteristics of the nanocomposite revealed that its electrical resistivity decreases with deposition time, with the lowest value obtained for 24 h of deposition. The cellulose–SnO2 hybrid nanocomposite can be used for biodegradable and disposable chemical, humidity and biosensors.

Dry Electroactive Paper Actuator Based on Cellulose/Poly(Ethylene Oxide)―Poly(Ethylene Glycol) MicroComposite

Cellulose Electroactive Paper (EAPap) is an attractive material to construct biomimetic actuators and MEMS devices due to its lightweight, biodegradability, large displacement, and low actuation voltage. However, the performance of the actuator is sensitive to humidity levels. In this article, cellulose/poly(ethylene oxide) (PEO)—poly(ethylene glycol) (PEG) microcomposites were fabricated for EAPap actuators working at ambient humidity condition, and the effect of different PEO : PEG ratios (0.95 : 0.05 to 0.99 : 0.01) on the actuation behavior was investigated. Based on the bending displacement, power consumption, and durability, 0.95 :0.05 ratio was identified as an optimum ratio of PEO : PEG to blend with cellulose for EAPap actuator. The actuation mechanism of the cellulose/PEO—PEG actuator was addressed.

Wirelessly driven electro-active paper actuator made with cellulose-polypyrrole-ionic liquid and dipole rectenna

This paper reports a wirelessly driven electro-active paper actuator that consists of a dipole rectenna array, a power control circuit and two cellulose–polypyrrole–ionic liquid (CPIL) electro-active paper actuators. The CPIL nanocomposite actuator was fabricated by incorporating nanoscaled PPy onto cellulose by an in situ polymerization technique, which was followed by activation in a room temperature ionic liquid. The CPIL actuator shows its maximum bending displacement of 10 mm at an ambient humidity condition with 30 mW electrical power consumption. The CPIL actuator is very stable in its actuator performance. The dipole rectenna array receives microwaves and converts them to dc power so as to wirelessly supply power to the actuators. Three flexible dipole rectenna arrays are designed, manufactured and characterized. The rectenna array that has nine rectenna elements generates the maximum power of 75 mW. This power was used to successfully activate the two CPIL actuators and the control circuit. Detailed fabrication and characterization of the CPIL actuator and the dipole rectenna array as well as the control circuit are explained.

Hybrid composite thin films composed of tin oxide nanoparticles and cellulose

This paper reports the preparation and characterization of hybrid thin films consisting of tin oxide (SnO2) nanoparticles and cellulose. SnO2 nanoparticle loaded cellulose hybrid thin films were fabricated by a solution blending technique, using sodium dodecyl sulfate as a dispersion agent. Scanning and transmission electron microscopy studies revealed uniform dispersion of the SnO2 nanoparticles in the cellulose matrix. Reduction in the crystalline melting transition temperature and tensile properties of cellulose was observed due to the SnO2 nanoparticle loading. Potential application of these hybrid thin films as low cost, flexible and biodegradable humidity sensors is examined in terms of the change in electrical resistivity of the material exposed to a wide range of humidity as well as its response–recovery behavior.

Influence of residual ionic liquid on the thermal stability and electromechanical behavior of cellulose regenerated from 1-ethyl-3-methylimidazolium acetate

The regenerated cellulose films were prepared by dissolving cotton cellulose pulp directly in room temperature ionic liquid namely, 1-ethyl-3-methylimidazolium acetate at 80 °C, followed by washing/curing in different coagulants namely, methanol, deionized water, methanol-deionized water, and isopropyl alcohol-deionized water. It was found that the type of coagulants employed for curing the cellulose films has a significant influence on the amount of residual ionic liquid entrapped in the films. The amount of residual ionic liquids was 2.68, 1.01, 0.84, and 0.75 wt.% for the films cured with deionized water, isopropyl alcohol-deionized water, methanol, and methanol-deionized water, respectively. The DTG peaks of regenerated cellulose films showed two decomposition temperatures at 280 °C and 320 °C. Among all the cases studied, deionized water curing case showed the lowest decomposition temperature, attributed to entrapment of large residual ionic liquid in it. Electromechanical characteristic of the regenerated cellulose films was also investigated.

An electro-active paper actuator made with cellulose–polypyrrole–ionic liquid nanocomposite: influence of ionic liquid concentration, type of anion and humidity

This paper reports a cellulose–polypyrrole–ionic liquid (CPIL) nanocomposite that can produce large actuating displacement in a low humidity environment. The fabrication process and actuator performance of the CPIL nanocomposite actuator are illustrated. Experimental results revealed that the size of anion, concentration of ionic liquid and ambient humidity level have a significant influence on the actuator performance of the CPIL nanocomposite. The bending displacement of the CPIL nanocomposite actuator was enhanced with increasing anion size, ionic liquid concentration and humidity level. CPIL nanocomposite made with 4% BMIBF4 ionic liquid exhibited a very large bending displacement with excellent durability under ambient conditions (30% relative humidity and 25 °C). This is probably the first report that cellulose based electro-active paper actuator can exhibit such a large bending displacement under ambient conditions. Experimental results revealed that the proposed CPIL nanocomposite actuator under study can be operated up to 70% humidity level.