Unhan Lee

Chonnam National University

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Hyeonseok Yoon

Chonnam National University

Eunseo Heo

Chonnam National University

Thanh‐Hai Le

Chonnam National University

Haney Lee

Chonnam National University

Semin Kim

Korea Research Institute of Chemical Technology

Sanghyuck Lee

Chung-Ang University

Subin Chae

Chonnam National University

Yunseok Choi

Washington University in St. Louis

Hyemi Jo

Chonnam National University

Chul Soon Park

Korea Advanced Institute of Science and Technology

Cooperative Institutions

Chonnam National University

Chonnam National University Hospital

Gwangju University

Graduate School USA

Seoul National University

Korea University

Korea Research Institute of Bioscience and Biotechnology

Hanyang University

Government of the Republic of Korea

MacDiarmid Institute for Advanced Materials and Nanotechnology

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Electrical monitoring of photoisomerization of block copolymers intercalated into graphene sheets

Nature Communications (2020)

Semin Kim Thanh‐Hai Le Yunseok Choi Haney Lee Eunseo Heo

Abstract Insulating polymers have received little attention in electronic applications. Here, we synthesize a photoresponsive, amphiphilic block copolymer (PEO- b -PVBO) and further control the chain growth of the block segment (PVBO) to obtain different degrees of polymerization (DPs). The benzylidene oxazolone moiety in PEO- b -PVBO facilitated chain-conformational changes due to photoisomerization under visible/ultraviolet (UV) light illumination. Intercalation of the photoresponsive but electrically insulating PEO- b -PVBO into graphene sheets enabled electrical monitoring of the conformational change of the block copolymer at the molecular level. The current change at the microampere level was proportional to the DP of PVBO, demonstrating that the PEO- b -PVBO-intercalated graphene nanohybrid (PGNH) can be used in UV sensors. Additionally, discrete signals at the nanoampere level were separated from the first derivative of the time-dependent current using the fast Fourier transform (FFT). Analysis of the harmonic frequencies using the FFT revealed that the PGNH afforded sawtooth-type current flow mediated by Coulomb blockade oscillation.

Moiety

10.1038/s41467-020-15132-z

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Citations (19)

Highly Elastic and >200% Reversibly Stretchable Down‐Conversion White Light‐Emitting Diodes Based on Quantum Dot Gel Emitters

Advanced Optical Materials (2020)

Thanh‐Hai Le Yunseok Choi Semin Kim Unhan Lee Eunseo Heo

Abstract Combining the characteristics of different materials offers exciting new opportunities for advanced applications in various fields. Herein, white light‐emitting diodes (WLEDs) with >200% reversible stretchability are fabricated using six‐color quantum dots (QDs) gel emitters. Stable aqueous‐phase alloy core/shell QDs with high quantum yield are obtained via ligand exchange using a ternary solvent system. Transparent and highly stretchable gels with large pores are created by binary‐solvent‐based gelation at low temperatures. Importantly, the QDs and the gel originate from the same two solvents, which make the QDs highly compatible with the gelation process. Consequently, QDs of six different colors are incorporated into the gel without any property degradation. The excellent optical properties of the QDs in the liquid phase (e.g., 17% higher photoluminescence (PL) intensity) are retained in the gel phase. The QD gel (QDG) exhibits elastic deformation up to 200%, with uniform PL over the entire gel. A down‐conversion WLED built using the QDG emitter produces cool white light with a color temperature of 6100 K, a color rendering index of 94, and a luminous efficacy of 72 lm W −1 . In addition, the performance of the QDG‐based WLED remains unchanged even after more than 1000 bending/stretching cycles.

Quantum yield

Luminous efficacy

10.1002/adom.201901972

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Surfactant‐in‐Polymer Templating: Surfactant‐in‐Polymer Templating for Fabrication of Carbon Nanofibers with Controlled Interior Substructures: Designing Versatile Materials for Energy Applications (Small 18/2021)

Small (2021)

Eunseo Heo Seonmyeong Noh Unhan Lee Thanh‐Hai Le Haney Lee

Adding only a surfactant to the polymer precursor leads to the creation of useful products with secondary substructures and functionality. As a model case, carbon nanofibers with interior ironin-pore substructures are demonstrated as versatile electrode materials and electrocatalysts by Hyeonseok Yoon and co-workers in article number 2007775.

Carbon fibers

10.1002/smll.202170084

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Anomalous restoration of sp² hybridization in graphene functionalization

Nanoscale (2020)

Subin Chae Thanh‐Hai Le Chul Soon Park Yunseok Choi Semin Kim

The functionalization of nanocarbon materials such as graphene has attracted considerable attention over the past decades.

Surface Modification

10.1039/d0nr03422c

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Citations (32)

Controlled anisotropic growth of layered perovskite nanocrystals for enhanced optoelectronic properties

Chemical Engineering Journal (2020)

Thanh‐Hai Le Sanghyuck Lee Eunseo Heo Unhan Lee Haney Lee

Photocurrent

Nanometre

Photoactive layer

10.1016/j.cej.2020.128045

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Citations (16)

Zero reduction luminescence of aqueous-phase alloy core/shell quantum dots via rapid ambient-condition ligand exchange

Journal of Colloid and Interface Science (2019)

Thanh‐Hai Le Semin Kim Subin Chae Yunseok Choi Chul Soon Park

Quantum yield

Aqueous two-phase system

10.1016/j.jcis.2019.12.104

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Citations (13)

Surfactant‐in‐Polymer Templating for Fabrication of Carbon Nanofibers with Controlled Interior Substructures: Designing Versatile Materials for Energy Applications

Small (2021)

Eunseo Heo Seonmyeong Noh Unhan Lee Thanh‐Hai Le Haney Lee

Abstract A simple, scalable, surfactant‐in‐polymer templating approach is demonstrated to create controlled long‐range secondary substructures in a primary structure. A metal bis(2‐ethylhexyl) sulfosuccinate (MAOT) as the surfactant is shown to be capable of serving as a sacrificial template and metal precursor in carbon nanofibers. The low interfacial tension and controllable dimensions of the MAOT are maintained in the solid‐phase polymer, even during electrospinning and heat‐treatment processes, allowing for the long‐range uniform formation of substructures in the nanofibers. The MAOT content is found to be a critical parameter for tailoring the diameter of the nanofibers and their textural properties, such as size and volume of interior pores. The metal counterion species in the MAOT determine the introduction of metallic phases in the nanofiber interior. The incorporation of MAOT with Na as the counterion into the polymer phase leads to the formation of a built‐in pore structure in the nanofibers. In contrast, MAOT with Fe as a counterion generates unique iron‐in‐pore substructures in the nanofibers (FeCNFs). The FeCNFs exhibit outstanding charge storage and water splitting performances. As a result, the MAOT‐in‐polymer templating approach can be extended to combinations of various metal precursors and thus create desirable functionalities for different target applications.

Electrospinning

10.1002/smll.202007775

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Citations (14)

Carbon dots for epoxy curing: Anti-forgery patterns with long-term luminescent stability

Chemical Engineering Journal (2020)

Unhan Lee Eunseo Heo Thanh‐Hai Le Haney Lee Semin Kim

Passivation

10.1016/j.cej.2020.126988

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Citations (31)