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Shape-Adaptable 2D Titanium Carbide (MXene) Heater
Park, Tae Hyun,Yu, Seunggun,Koo, Min,Kim, Hyerim,Kim, Eui Hyuk,Park, Jung-Eun,Ok, Byeori,Kim, Byeonggwan,Noh, Sung Hyun,Park, Chanho,Kim, Eunkyoung,Koo, Chong Min,Park, Cheolmin American Chemical Society 2019 ACS NANO Vol.13 No.6
<P>Prior to the advent of the next-generation heater for wearable/on-body electronic devices, various properties are required, including conductivity, transparency, mechanical reliability, and conformability. Expansion to two-dimensional (2D) structure of metallic nanowires based on network- and mesh-type geometries has been widely exploited for realizing these heaters. However, the routes led to many drawbacks such as the low-density cross-bar linking, self-aggregation of wire, and high junction resistance. Although 2D carbon nanomaterials such as graphene and reduced graphene oxide (rGO) have shown their potentials for the purpose, CVD-grown graphene with sufficiently high conductivity was limited due to its poor processability for large-area applications, while rGO fabricated with a complex reduction process involving the use of toxic chemicals suffered from a low electrical conductivity. In this study, we demonstrate a simple and robust process, utilizing electrostatic assembling of negatively charged MXene flakes on a positively treated surface of substrate, for fabricating a metal-like 2D MXene thin film heater (TFH). Our TFH showed a high optical property (>65%), low sheet resistance (215 ?/sq), fast electrothermal response (within dozens of seconds) with an intrinsically high electrical conductivity, and mechanical flexibility (up to 180? bending). Its capability for forming a firm and stable ionic-type interface with a counterpart surface allows us to develop a shape-adaptable and patchable thread heater (TH) that can be shaped on diverse substrates even under harsh conditions of conventional sewing or weaving processes. This work suggests that our shape-adaptable MXene heaters are potentially suitable not only for wearable devices for local heating and defrosting but also for a variety of emerging applications of soft actuators and wearable/flexible healthcare monitoring and thermotherapy.</P> [FIG OMISSION]</BR>
Electrically Tunable Soft-Solid Block Copolymer Structural Color
Park, Tae Joon,Hwang, Sun Kak,Park, Sungmin,Cho, Sung Hwan,Park, Tae Hyun,Jeong, Beomjin,Kang, Han Sol,Ryu, Du Yeol,Huh, June,Thomas, Edwin L.,Park, Cheolmin American Chemical Society 2015 ACS NANO Vol.9 No.12
<P>One-dimensional photonic crystals based on the periodic stacking of two different dielectric layers have been widely studied, but the fabrication of mechanically flexible polymer structural color (SC) films, with electro-active color switching, remains challenging. Here, we demonstrate free-standing electric field tunable ionic liquid (IL) swollen block copolymer (BCP) films. Placement of a polymer/ionic liquid film-reservoir adjacent to a self-assembled poly(styrene-<I>block</I>-quaternized 2-vinylpyridine) (PS-<I>b</I>-QP2VP) copolymer SC film allowed the development of red (R), green (G), and blue (B) full-color SC block copolymer films by swelling of the QP2VP domains by the ionic liquid associated with water molecules. The IL–polymer/BCP SC film is mechanically flexible with excellent color stability over several days at ambient conditions. The selective swelling of the QP2VP domains could be controlled by both the ratio of the IL to a polymer in the gel-like IL reservoir layer and by an applied voltage in the range of −3 to +6 V using a metal/IL reservoir/SC film/IL reservoir/metal capacitor type device.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-12/acsnano.5b05234/production/images/medium/nn-2015-052345_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b05234'>ACS Electronic Supporting Info</A></P>
Cheolmin Park,Jinho Chang 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.12
Zn-polyiodide redox flow battery is considered to be promising energy storage systems. However, the rate of the I3?(aq)/I?(aq) half redox reaction could be limited by a metastable iodine film in aqueous solutions. In this article, we found that the addition of Br? could inhibit the formation of an iodine film (I2-F) and form soluble I2Br?(aq) during the electrooxidation of I?. I? was electrochemically oxidized to the soluble form I3?(aq). The depletion of I?(aq) and an increase of I3?(aq) would lead to the formation of I2 and form I2-F. Then, under a steady state, I?(aq) was electrochemically oxidized to I3?(aq) via I2-F. However, the reaction pathway for the electrooxidation of I? was significantly altered by the addition of Br?. I? was electrochemically oxidized to I3?(aq) and was further oxidized to I2Br?(aq) without the formation of I2-F. Moreover, we estimated the stability constant of I2Br?(aq) and consequently the fractional diagrams of I2(aq), I3?(aq), and I2Br?(aq) existing in a solution with both I? and Br? during the electrooxidation of I?, providing the necessity of a highly concentrated Br? condition in the vicinity of an electrode to form I2Br?(aq) as the main iodine species through the electrooxidation of I?.
Rewritable, Printable Conducting Liquid Metal Hydrogel
Park, Jung-Eun,Kang, Han Sol,Baek, Jonghyek,Park, Tae Hyun,Oh, Seunghee,Lee, Hyungsuk,Koo, Min,Park, Cheolmin American Chemical Society 2019 ACS NANO Vol.13 No.8
<P>The development of high-performance printable electrical circuits, particularly based on liquid metals, is fundamental for device interconnection in flexible electronics, motivating numerous attempts to develop a variety of alloys and their composites. Despite their great potential, rewritable and printable electronic circuits based on liquid metals are still manufactured on demand. In this study, we demonstrate liquid metal-based hydrogels suitable for rewritable, printable electrical circuits. Our liquid metal hydrogels are based on sedimentation-induced composites of eutectic gallium-indium (EGaIn) particles in poly(ethylene glycol) diacrylate (PEGDA). The EGaIn particles are vertically phase-segregated in the PEGDA. When a composite surface with high EGaIn content is gently scratched, the surface covering PEGDA is removed, followed by the rupture of the native oxide layers of the particles, and the exposed EGaIn becomes conductive. The subsequent water-driven swelling of PEGDA on the scratched surface completely erases the conductive circuit, causing the system to reset. Our friction-responsive liquid metal hydrogel exhibits writing-erasing endurance for 20 cycles, with a dramatic change in the electrical resistance from metal (∼1 Ω) to insulator (∼10<SUP>7</SUP> Ω). By employing surface friction pen printing, we demonstrate mechanically flexible, rewritable, printable electrical conductors suitable for displays.</P> [FIG OMISSION]</BR>
Park, Sungmin,Koo, Kyosung,Kim, Kyunginn,Ahn, Hyungju,Lee, Byeongdu,Park, Cheolmin,Ryu, Du Yeol Elsevier 2015 Polymer Vol.60 No.-
<P><B>Abstract</B></P> <P>The phase transitions in the films of an asymmetric polystyrene-<I>b</I>-poly(2-vinylpyridine) (PS-<I>b</I>-P2VP) were investigated by grazing incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). Compared with the sequential transitions in the bulk, hexagonally perforated layer (HPL) – gyroid (GYR) – disorder (DIS) upon heating, the transitions in film geometry were dramatically changed with decreasing thickness due to the growing preferential interactions from substrate, resulting in a thickness-dependent transition diagram including four different morphologies of hexagonally modulated layer (HML), coexisting (HML and GYR), GYR, and DIS. Particularly in the films ≤10<I>L</I> <SUB> <I>o</I> </SUB>, where <I>L</I> <SUB> <I>o</I> </SUB> is <I>d</I>-spacing at 150 °C, a stable HML structure was identified even above the order-to-disorder transition (ODT) temperature of the bulk, which was attributed to the suppressed compositional fluctuations by the enhanced substrate interactions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phase transitions in the bulk and films of asymmetric polystyrene-<I>b</I>-poly(2-vinylpyridine). </LI> <LI> Significant change in transitions of the films with decreasing film thickness. </LI> <LI> New observation of hexagonally modulated layer (HML) morphology in film geometry. </LI> <LI> A stable HML structure extended over the entire temperature range in the films ≤10<I>L</I> <SUB> <I>o</I> </SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>