Kwang Jin Kim

Transparent actuator made with few layer graphene electrode and dielectric elastomer, for variable focus lens

A transparent dielectric elastomer actuator driven by few-layer-graphene (FLG) electrode was experimentally investigated. The electrodes were made of graphene, which was dispersed in N-methyl-pyrrolidone. The transparent actuator was fabricated from developed FLG electrodes. The FLG electrode with its sheet resistance of 0.45u2009kΩ/sq (80u2009nm thick) was implemented to mask silicone elastomer. The developed FLG-driven actuator exhibited an optical transparency of over 57% at a wavenumber of 600u2009nm and produced bending displacement performance ranging from 29 to 946u2009μm as functions of frequency and voltage. The focus variation was clearly demonstrated under actuation to study its application-feasibility in variable focus lens and various opto-electro-mechanical devices.

An ionic electro-active actuator made with graphene film electrode, chitosan and ionic liquid

A newly developed ionic electro-active actuator composed of an ionic electrolyte layer sandwiched between two graphene film layers was investigated. Scanning electronic microscopy observation and x-ray diffraction analysis showed that the graphene sheets in the film stacked in a nearly face-to-face fashion but did not restack back to graphite, and the resulting graphene film with low sheet resistance (10 Ω sq−1) adheres well to the electrolyte membrane. Contact angle measurement showed the surface energy (37.98 mJ m−2) of the ionic electrolyte polymer is 2.67 times higher than that (14.2 mJ m−2) of the Nafion membrane, contributing to the good adhesion between the graphene film electrode and the electrolyte membrane. An electric double-layer is formed at the interface between the graphene film electrode and the ionic electrolyte membrane under the input potential, resulting in a higher capacitance of 27.6 mF cm−2. We report that this ionic actuator exhibits adequate bending strain, ranging from 0.032 to 0.1% (305 to 945 μm) as functions of voltage.

Biomimetic robotic artificial muscles

Introduction Physical Principles of Ionic Polymer-Metal Composites New IPMC Materials and Mechanisms A Systems Perspective on Modeling of Ionic Polymer-Metal Composites Conjugated Polymer Actuators: Modeling and Control Synthetic Dielectric Elastomer Materials Dielectric Elastomer Actuator Integrated Sensory Feedback for EAP Actuators Device and Robotic Applications of EAPs.

Noncovalently assembled nanotubular porous layers for delaying of heating surface failure

Thermal management to prevent extreme heat surge in integrated electronic systems and nuclear reactors is a critical issue. To delay the thermal surge on the heater effectively, we report the benefit of a three dimensional nanotubular porous layer via noncovalent interactions (hydrophobic forces and hydrogen bonds). To observe the contribution of individual noncovalent interactions in a porous network formation, pristine carbon nanotubes (PCNTs) and oxidatively functionalized carbon nanotubes (FCNTs) were compared. Hydrogen-bonded interwoven nanotubular porous layer showed approximately two times critical heat flux (CHF) increase compared to that of a plain surface. It is assumed that the hydrophilic group-tethered nanotubular porous wicks and enhanced fluidity are the main causes for promoting the CHF increase. Reinforced hydrophilicity assists liquid spreading and capillarity-induced liquid pumping, which are estimated by using Electrochemical Impedance Spectroscopy. Also, shear induced thermal conduction, thermal boundary reduction, and rheology of nanoparticles could attribute to CHF enhancement phenomena.

Toward nano-biomimetic muscles: polyacrylonitrile nanofibers

The important characteristics of the activated Polyacrylonitrile (PAN) fibers are its ability to change in length more than 100% and its comparable strength to human muscle. As against to other reported works in which commercially available fibers with diameters in the range of 10s of micrometers were used, here we tried to study the phenomenon in a few hundred nanometer diameter fibers. These fibers are expected to have smaller response times and higher deformations than conventional micronsized fibers. These PAN fibers were made by electrospinning. The fibers are placed in a solution and the change in the shape of the fibers was observed with change in pH. The fibers contracted in acidic solution and expanded in basic solution similar to that reported in the literature. Here we measured the variation in the diameter of the fibers using E-SEM while the change in pH is taking place. It appears that a variation of more than 100% was observed similar to that observed with conventional fibers of diameter ranging from 10 to 50mm. These results provide a potential in developing fast actuating PAN muscles and linear acuators, and muscle structures similar to sarcomere/myosin/actin-like assembly. In addition, we were able to observe giant volume changes more than 1,000% with conventional PAN fibers.

All Biomass and UV Protective Composite Composed of Compatibilized Lignin and Poly (Lactic-acid)

Utilization of carbon-neutral biomass became increasingly important due to a desperate need for carbon reduction in the issue of global warming in light of replacing petroleum-based materials. We used lignin, which was an abundant, low cost, and non-food based biomass, for the development of all biomass-based films and composites through reactive compatibilization with poly (lactic-acid) (PLA). Using a facile and practical route, the hydrophilic hydroxyl groups of lignin were acetylated to impose the compatibility with PLA. The solubility parameter of the pristine lignin at 26.3 (J/cm3)0.5 was altered to 20.9 (J/cm3)0.5 by acetylation allowing the good compatibility with PLA at 20.2 (J/cm3)0.5. The improved compatibility of lignin and PLA provided substantially decreased lignin domain size in composites (12.7u2009μm), which subsequently gave transparent and UV-protection films (visual transmittance at 76% and UV protection factor over 40). The tensile strength and elongation of the developed composite films were increased by 22% and 76%, respectively, and the biobased carbon content was confirmed as 96u2009±u20093%. The developed PLA/lignin composites provided 100% all-biomass contents and balanced optical and mechanical properties that could broaden its eco-friendly applications in various industries.