Effects of Hexagonal Boron Nitride Insulating Layers on the Driving Performance of Ionic Electroactive Polymer Actuators for Light-Weight Artificial Muscles.

To improve the energy efficiency and driving performance of ionic electroactive polymer actuators, we propose inserting insulating layers of 170 nm hexagonal boron nitride (h-BN) particles between the ionic polymer membrane and electrodes. In experiments, actuators exhibited better capacitance (4.020 × 10-1 F), displacement (6.01 mm), and curvature (35.59 m-1) with such layers than without them. The excellent insulating properties and uniform morphology of the layers reduced the interfacial resistance, and the ion conductivity (0.071 S m-1) within the ionic polymer improved significantly. Durability was enhanced because the h-BN layer is chemically and thermally stable and efficiently blocks heat diffusion and ion hydrate evaporation during operation. The results demonstrate a close relationship between the capacitance and driving performance of actuators. A gripper prepared from the proposed ionic electroactive polymer actuator can stably hold an object even under strong external vibration and fast or slow movement.

Synthesis of Three-Dimensional Carbon Nanostructure/Copper Nanowire for Additive Interface Layer of Ionic Polymer Metal Composite.

Additive interface materials for improved ionic polymer metal composite (IPMC) actuator performance are being investigated. In this study, three-dimensional carbon nanostructure/copper nanowire (3DC Cu-NW) with a novel structure was synthesized via low-pressure chemical vapor deposition. An IPMC actuator with a 3DC Cu-NW interface layer was fabricated, which exhibited improved actuation performance, long-term stability, and electrochemical properties. The proposed 3DC consists of carbon nanotubes (CNTs) and graphene, grown using an Fe catalyst and CH4 gas, respectively. We optimized the growth conditions (Fe catalyst: 12.5 mg/L, CH4: 20 sccm) to achieve a 3DC with an appropriate thickness and a large specific surface area. The 3DC Cu-NW benefited from a Cu oxidation prevention property and a large specific surface area. The electrochemical properties and actuation performance of the IPMC actuator improved with an increased 3DC Cu-NW concentration. An IPMC actuator with a 0.6 wt% 3DC Cu-NW interface layer exhibited 1.3- and 5.6-fold electrochemical property and actuation performance improvement, respectively, over an IPMC actuator with no 3DC Cu-NW interface layer. These results show that the proposed 3DC Cu-NW has potential as an IPMC actuator interface material, and that 3DC Cu-NW synthesis and application technology can be applied to future research on sensor, actuator, and flexible devices.

Effect of Ionic Polymer Membrane with Multiwalled Carbon Nanotubes on the Mechanical Performance of Ionic Electroactive Polymer Actuators.

Ionic electroactive polymer (IEAP) actuators have received interest because of their advantageous properties, including their large displacement, high energy density, light weight, and low power consumption under a low electric field. However, they have a low blocking force under driving, and it is difficult to control the thickness of the ionic polymer membrane. In this study, an IEAP actuator is fabricated using a Nafion membrane with added multiwalled carbon nanotubes to increase the blocking force. A heat press two-step process is also developed to produce a constant and uniform membrane. The fabricated Nafion membrane with 0.2 wt% multiwalled carbon nanotubes has the largest displacement and highest blocking force. As a result, the developed heat press two-step method can be used in various polymer-casting fields, and the fabricated carbon nanotube-based IEAP actuators can serve as useful references in fields such as flexible robotics and artificial muscles.

Synthesis of Nitrogen-Doped Graphene on Copper Nanowires for Efficient Thermal Conductivity and Stability by Using Conventional Thermal Chemical Vapor Deposition.

Cu nanowires (NWs) possess remarkable potential a slow-cost heat transfer material in modern electronic devices. However, Cu NWs with high aspect ratios undergo surface oxidation, resulting in performance degradation. A growth temperature of approximately <1000 °C is required for preventing the changing of Cu NW morphology by the melting of Cu NWs at over 1000 °C. In addition, nitrogen (N)-doped carbon materials coated on Cu NWs need the formation hindrance of oxides and high thermal conductivity of Cu NWs. Therefore, we investigated the N-doped graphene-coated Cu NWs (NG/Cu NWs) to enhance both the thermal conductivity and oxidation stability of Cu NWs. The Cu NWs were synthesized through an aqueous method, and ethylenediamine with an amine group induced the isotropic growth of Cu to produce Cu NWs. At that time, the amine group could be used as a growth source for the N-doped graphene on Cu NWs. To grow an N-doped graphene without changing the morphology of Cu NWs, we report a double-zone growth process at a low growth temperature of approximately 600 °C. Thermal-interface material measurements were conducted on the NG/Cu NWs to confirm their applicability as heat transfer materials. Our results show that the synthesis technology of N-doped graphene on Cu NWs could promote future research and applications of thermal interface materials in air-stable flexible electronic devices.

Enhanced Stability and Driving Performance of GO⁻Ag-NW-based Ionic Electroactive Polymer Actuators with Triton X-100-PEDOT:PSS Nanofibrils.

Ionic electroactive polymers (IEAPs) have received considerable attention for their flexibility, lightweight composition, large displacement, and low-voltage activation. Recently, many metal-nonmetal composite electrodes have been actively studied. Specifically, graphene oxide-silver nanowire (GO-Ag NW) composite electrodes offer advantages among IEAPs with metal-nonmetal composite electrodes. However, GO-Ag NW composite electrodes still show a decrease in displacement owing to low stability and durability during driving. Therefore, the durability and stability of the IEAPs with metal-nonmetal composite electrodes must be improved. One way to improve the device durability is coating the electrode surface with a protective layer. This layer must have enough flexibility and suitable electrical properties such that it does not hinder the IEAPs' driving. Herein, a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) protective layer and 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100) are applied to improve driving performance. Triton X-100 is a nonionic surfactant that transforms the PEDOT:PSS capsule into a nanofibril structure. In this study, a mixed Triton X-100/PEDOT:PSS protective layer at an optimum weight ratio was coated onto the GO-Ag NW composite-electrode-based IEAPs under various conditions. The IEAP actuators based on GO-Ag NW composite electrodes with a protective layer of PEDOT:PSS treated with Triton X-100 showed the best stability and durability.

Fast and Stable Ionic Electroactive Polymer Actuators with PEDOT:PSS/(Graphene⁻Ag-Nanowires) Nanocomposite Electrodes.

Ionic electroactive polymer (IEAP) actuators that are driven by electrical stimuli have been widely investigated for use in practical applications. However, conventional electrodes in IEAP actuators have a serious drawback of poor durability under long-term actuation in open air, mainly because of leakage of the inner electrolyte and hydrated cations through surface cracks on the metallic electrodes. To overcome this problem, a top priority is developing new high-performance ionic polymer actuators with graphene electrodes that have superior mechanical, electrical conductivity, and electromechanical properties. However, the task is made difficultby issues such as the low electrical conductivity of graphene (G). The percolation network of silver nanowires (Ag-NWs) is believed to enhance the conductivity of graphene, while poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which exhibits excellent stability under ambient conditions, is expected to improve the actuation performance of IEAP actuators. In this study, we developed a very fast, stable, and durable IEAP actuator by employing electrodes made of a nanocomposite comprising PEDOT:PSS and graphene⁻Ag-NWs (P/(G⁻Ag)). The cost-effective P/(G⁻Ag) electrodes with high electrical conductivity displayed a smooth surface resulting from the PEDOT:PSS coating, which prevented oxidation of the surface upon exposure to air, and showedstrong bonding between the ionic polymer and the electrode surface. More interestingly, the proposed IEAP actuator based on the P/G⁻Ag electrode can be used in active biomedical devices, biomimetic robots, wearable electronics, and flexible soft electronics.

Microfluidic technologies for circulating tumor cell isolation.

Metastasis is the main cause of tumor-related death, and the dispersal of tumor cells through the circulatory system is a critical step in the metastatic process. Early detection and analysis of circulating tumor cells (CTCs) is therefore important for early diagnosis, prognosis, and effective treatment of cancer, enabling favorable clinical outcomes in cancer patients. Accurate and reliable methods for isolating and detecting CTCs are necessary to obtain this clinical information. Over the past two decades, microfluidic technologies have demonstrated great potential for isolating and detecting CTCs from blood. The present paper reviews current advanced microfluidic technologies for isolating CTCs based on various biological and physical principles, and discusses their fundamental advantages and drawbacks for subsequent cellular and molecular assays. Owing to significant genetic heterogeneity among CTCs, microfluidic technologies for isolating individual CTCs have recently been developed. We discuss these single-cell isolation methods, as well as approaches to overcoming the limitations of current microfluidic CTC isolation technologies. Finally, we provide an overview of future innovative microfluidic platforms.

Fabrication and Characterization of Graphene-Based Electrochemical Sensors for Glucose Measurement.

Glucose in the blood is generally measured by electrochemical method using glucose oxidase (GOx) which acts as enzymes and reduced graphene oxide (rGO) composite. The rGO, which has low dispersibility, reduces the sensing capability of sensors. In order to solve this problem, the rGO electrodes with the addition of polyvinylpyrrolidone (PVP) have been reported. However, rGO with low electrical conductivity and mobility is not compatible to the electrochemical system. In this study, graphene with excellent electrical properties was added to PVP protected rGO. The rGO was synthesized using a Hummer and Offeman's method. Graphene was synthesized using chemical vapor deposition (CVD) with a Cu catalyst. Platinum (Pt) electrodes, Ag/AgCl, and PVP protected rGO were used as working electrode, reference electrode, and counter electrode, respectively. Surface morphology and structural properties of graphene were analyzed using atomic force microscopy (AFM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). Cyclic voltametry (CV) and I-V probe station were used to analyze the performance of the electrodes. Glucose concentration was systematically varied and the reduction current was monitored using I-V probe station.

Effects of the electrical conductivity and orientation of silicon substrate on the synthesis of multi-walled carbon nanotubes by thermal chemical vapor deposition.

We studied the effects of the electrical conductivity and orientation of silicon substrate on both catalytic Fe thin film and the structure and morphology of multi-walled carbon nanotube (MWNT) grown by low-pressure chemical vapor deposition. Both p-type Si(100) and Si(111) substrates with three different doping concentrations (high, low, undoped) were used to evaluate the formation of catalytic nanoparticles and the growth of MWNTs. The morphology of catalytic nanoparticles such as size and density was characterized by field-emission scanning electron microscopy, Cs-corrected energy-filtered transmission electron microscopy, and X-ray photoelectron spectroscopy. Structural characteristics of MWNTs grown on different combinations of silicon substrate orientation and electrical conductivities (σ) were also systematically analyzed. Based on the experimental results, growth modes of MWNTs could be controlled by choosing an appropriate combination of σ and orientation of Si substrates.

Fabrication and characterization of carbon-based counter electrodes prepared by electrophoretic deposition for dye-sensitized solar cells.

Three different carbon-based counter electrodes are investigated in light of catalytic activities such as electrochemical frequencies and interface impedances. We fabricated carbon-based counter electrodes of dye-sensitized solar cells [DSSCs] using graphene, single-walled carbon nanotubes [SWNTs], and graphene-SWNT composites by electrophoretic deposition method. We observed the optical and electrochemical properties of the carbon-based counter electrodes. The DSSC with the graphene-deposited counter electrode demonstrated the best conversion efficiency of 5.87% under AM 1.5 and 1 sun condition. It could be utilized for a low-cost and high-throughput process for DSSCs.

Enhanced field emission from aligned multistage carbon nanotube emitter arrays.

In this work we report on the synthesis and field emission properties of carbon nanotube multistage emitter arrays grown on porous silicon by catalytic thermal chemical vapor deposition. The vertically oriented multistage array structures consisted of SWNTs and thin MWNTs grown on MWNTs, confirmed by TEM and Raman analysis. Higher field emission current ∼32 times and low threshold field ∼1.5 times were obtained for these structures in comparison to only MWNT arrays. The enhanced field emission results for these multistage emitters are a consequence of higher field concentration, which is ∼3 times more than MWNTs.

The effect of environmental factors on the electrical conductivity of a single oligo-DNA molecule measured using single-walled carbon nanotube nanoelectrodes.

We present an electrical conductivity study on a double-stranded DNA molecule bridging a single-walled carbon nanotube (SWNT) gap. The amine terminated DNA molecule was trapped between carboxyl functionalized SWNT electrodes by dielectrophoresis. The conductivity of DNA was measured while under the influence of various environmental factors, including salt concentration, counterion variation, pH and temperature. Typically, a current of tens of picoamperes at 1 V was observed at ambient conditions, with a decrease in conductance of about 33% in high vacuum conditions. The counterion variation was analyzed by changing the buffer from sodium acetate to tris(hydroxymethyl) aminomethane, which resulted in a two orders of magnitude increase in the conductivity of the DNA. A reversible shift in the current signal was observed for pH variation. An increase in conductivity of the DNA was also observed at high salt concentrations.