Yeon Sik Choi

AC Field-Induced Polymer Electroluminescence with Single Wall Carbon Nanotubes

We developed a high-performance field-induced polymer electroluminescence (FPEL) device consisting of four stacked layers: a top metal electrode/thin solution-processed nanocomposite film of single wall carbon nanotubes (SWNTs) and a fluorescent polymer/insulator/transparent bottom electrode working under an alternating current (AC) electric field. A small amount of SWNTs that were highly dispersed in the fluorescent polymer matrix by a conjugate block copolymer dispersant significantly enhanced EL, and we were able to realize an SWNT-FPEL device with a light emission of approximately 350 cd/m(2) at an applied voltage of ±25 V and an AC frequency of 300 kHz. The brightness of the SWNT-FPEL device is much greater than those of other AC-based organic or even inorganic ELs that generally require at least a few hundred volts. Light is emitted from our SWNT-FPEL device because of the sequential injection of field-induced holes and then electron carriers through ambipolar carbon nanotubes under an AC field, followed by exciton formation in the conjugated organic layer. Field-induced bipolar charge injection provides great material design freedom for our devices; the energy level does not have to be aligned between the electrode and the emission layer, and the balance of the carrier injected and transported can be altered in contrast to that in conventional organic light-emitting diodes, leading to an extremely cost-effective and unified device architecture that is applicable to all red-green-blue fluorescent polymers.

High Performance AC Electroluminescence from Colloidal Quantum Dot Hybrids

High performance field-induced AC electroluminescence (EL) in a simple ITO/insulator/hybrid emitter/Au structure was demonstrated with efficient control of the brightness and colors based on solution-processed nanohybrids of CdSe-ZnS core-shell colloidal quantum dots and fluorescent polymers.

Electroactive polymers for sensing

Electromechanical coupling in electroactive polymers (EAPs) has been widely applied for actuation and is also being increasingly investigated for sensing chemical and mechanical stimuli. EAPs are a unique class of materials, with low-moduli high-strain capabilities and the ability to conform to surfaces of different shapes. These features make them attractive for applications such as wearable sensors and interfacing with soft tissues. Here, we review the major types of EAPs and their sensing mechanisms. These are divided into two classes depending on the main type of charge carrier: ionic EAPs (such as conducting polymers and ionic polymer–metal composites) and electronic EAPs (such as dielectric elastomers, liquid-crystal polymers and piezoelectric polymers). This review is intended to serve as an introduction to the mechanisms of these materials and as a first step in material selection for both researchers and designers of flexible/bendable devices, biocompatible sensors or even robotic tactile sensing units.

A triboelectric generator based on self-poled Nylon-11 nanowires fabricated by gas-flow assisted template wetting

Triboelectric generators have emerged as potential candidates for mechanical energy harvesting, relying on motion-generated surface charge transfer between materials with different electron affinities. In this regard, synthetic organic materials with strong electron-donating tendencies are far less common than their electron-accepting counterparts. Nylons are notable exceptions, with odd-numbered Nylons such as Nylon-11, exhibiting electric polarisation that could further enhance the surface charge density crucial to triboelectric generator performance. However, the fabrication of Nylon-11 in the required polarised δ′-phase typically requires extremely rapid crystallisation, such as melt-quenching, as well as “poling” via mechanical stretching and/or large electric fields for dipolar alignment. Here, we propose an alternative one-step, near room-temperature fabrication method, namely gas-flow assisted nano-template (GANT) infiltration, by which highly crystalline “self-poled” δ′-phase Nylon-11 nanowires are grown from solution within nanoporous anodised aluminium oxide (AAO) templates. Our gas-flow assisted method allows for controlled crystallisation of the δ′-phase of Nylon-11 through rapid solvent evaporation and an artificially generated extreme temperature gradient within the nanopores of the AAO template, as accurately predicted by finite-element simulations. Furthermore, preferential crystal orientation originating from template-induced nano-confinement effects leads to self-poled δ′-phase Nylon-11 nanowires with higher surface charge distribution than melt-quenched Nylon-11 films, as observed by Kelvin probe force microscopy (KPFM). Correspondingly, a triboelectric nanogenerator (TENG) device based on as-grown templated Nylon-11 nanowires fabricated via GANT infiltration showed a ten-fold increase in output power density as compared to an aluminium-based triboelectric generator, when subjected to identical mechanical excitations.

Efficient Room‐Temperature Near‐Infrared Detection with Solution‐Processed Networked Single Wall Carbon Nanotube Field Effect Transistors

Efficient room temperature NIR detection with sufficient current gain is made with a solution-processed networked SWNT FET. The high performance NIR-FET with significantly enhanced photocurrent by more than two orders of magnitude compared to dark current in the depleted state is attributed to multiple Schottky barriers in the network, each of which absorb NIR and effectively separate photocarriers to corresponding electrodes.

Research data supporting [The effect of crystal structure on the electromechanical properties of piezoelectric Nylon-11 nanowires]

Research data supporting_Nylon NW SPM.zip file contains original SEM images and experimental data in the main text of the manuscript and supporting information. The original SEM images contain original scales and beam conditions at which SEM images were taken. raw-data.xlsx contains data files for the graphs, such as XRD, QNM, and PFM characterization, discussed in the main text of the manuscript and the supporting information.

Research data supporting 'Controlling and assessing the quality if aerosol jet printed features for large area and flexible electronics'

This dataset contains the raw resistance data collected from the printed samples. The raw SEM images and profilometer data used for the line width analysis are included, as well as the MATLAB code used to perform the analysis.

Research data supporting [A Triboelectric Generator Based on Self-poled Nylon-11 Nanowires Fabricated by Gas-flow Assisted Template Wetting]

Research data supporting_Nylon NW TENG.zip file contains original SEM images and experimental data in the main text of the manuscript and supporting information. The original SEM images contain original scales and beam conditions at which SEM images were taken. raw-data.xlsx contains data files for the graphs, such as XRD, DSC, energy harvesting measurements and electrical characterization, discussed in the main text of the manuscript and the supporting information.

Research data supporting "Piezoelectric Nylon-11 Nanowire Arrays Grown by Template Wetting for Vibrational Energy Harvesting Applications"

Figures Text.zip file contains original SEM images and graphical images included in the main text of the manuscript. The original SEM images contain original scales and beam conditions at which SEM images were taken. SEM images in the manuscript may have been taken as a whole or a part of the original images wherever apply. Likewise the scale in the manuscript images have been re‐drawn in order to enhance the clarity of the images, but depict true scale as they were in original. Supporting Information.zip contains original SEM images and graphical images included in the supporting information. The original SEM images contain original scales and beam conditions at which SEM images were taken. SEM images in the manuscript may have been taken as a whole or a part of the original images wherever apply. Likewise the scale in the manuscript images have been re‐drawn in order to enhance the clarity of the images, but depict true scale as they were in original. Raw data.xlsx contains data files for the graphs discussed in the main text of the manuscript and the supporting information.

The influence of microstructure of carbon nanotubes on the degree of length reduction during melt processing with polycarbonate

The length of fiber has strong effect on mechanical strength of fiber reinforced polymer nanocomposites. Previous work has shown that the length of multi-walled carbon nanotubes are reduced during melt mixing process with polyamide 6, 6. In this work, MWCNT/polycarbonate (PC) composites were prepared with four types of MWCNTs by injection molding. The severe melt mixing condition for dispersion of MWCNTs in the polymer matrix resulted in length reduction of MWCNTs. The microstructure and morphological properties of MWCNTs that influenced the degree of breakage and length reduction were experimentally investigated.