research
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Fabrication of Shape-conformable Batteries with 3D-Printing
(from left: Dr. Bok Yeop Ahn, Dr. Chanhoon Kim, Professor Il-Doo Kim and Professor Jennifer A. Lewis)
Flexible, wireless electronic devices are rapidly emerging and have reached the level of commercialization; nevertheless, most of battery shapes are limited to either spherical and/or rectangular structures, which results in inefficient space use. Professor Il-Doo Kim’s team from the Department of Materials Science at KAIST has successfully developed technology to significantly enhance the variability of battery design through collaboration research with Professor Jennifer A. Lewis and her team from the School of Engineering and Applied Sciences at Harvard University.
Most of the battery shapes today are optimized for coin cell and/or pouch cells. Since the battery as an energy storage device occupies most of the space in microelectronic devices with different designs, new technology to freely change the shape of the battery is required.
The KAIST-Harvard research collaboration team has successfully manufactured various kinds of battery shapes, such as ring-type, H, and U shape, using 3D printing technology. And through the research collaboration with Dr. Youngmin Choi at the Korea Research Institute of Chemical Technology (KRICT), 3D-printed batteries were applied to small-scale wearable electronic devices (wearable light sensor rings).
The research group has adopted environmentally friendly aqueous Zn-ion batteries to make customized battery packs. This system, which uses Zn2+ instead of Li+ as charge carriers, is much safer compared with the conventional lithium rechargeable batteries that use highly inflammable organic electrolytes. Moreover, the processing conditions of lithium-ion batteries are very complicated because organic solvents can ignite upon exposure to moisture and oxygen.
As the aqueous Zn-ion batteries adopted by the research team are stable upon contact with atmospheric moisture and oxygen, they can be fabricated in the ambient air condition, and have advantages in packaging since packaged plastic does not dissolve in water even when plastic packaging is applied using a 3D printer.
To fabricate a stable cathode that can be modulated in various forms and allows high charge-discharge, the research team fabricated a carbon fiber current collector using electrospinning process and uniformly coated electrochemically active polyaniline conductive polymer on the surface of carbon fiber for a current collector-active layer integrated cathode. The cathode, based on conductive polyaniline consisting of a 3D structure, exhibits very fast charging speeds (50% of the charge in two minutes) and can be fabricated without the detachment of active cathode materials, so various battery forms with high mechanical stability can be manufactured.
Prof. Kim said, “Zn-ion batteries employing aqueous electrolytes have the advantage of fabrication under ambient conditions, so it is easy to fabricate the customized battery packs using 3D printing.”
“3D-printed batteries can be easily applied for niche applications such as wearable, personalized, miniaturized micro-robots, and implantable medical devices or microelectronic storage devices with unique designs,” added Professor Lewis.
With Dr. Chanhoon Kim in the Department of Materials Science and Engineering at KAIST and Dr. Bok Yeop Ahn School of Engineering and Applied Sciences at Harvard University participating as equally contributing first authors, this work was published in the December issue of ACS Nano.
This work was financially supported by the Global Research Laboratory (NRF-2015K1A1A2029679) and Wearable Platform Materials Technology Center (2016R1A5A1009926).
Figure 1.Fabrication of shape-conformable batteries based on 3D-printing technology and the application of polyaniline carbon nanofiber cathodes and wearable electronic devices
Figure 2.Fabricated shape-conformable batteries based on a 3D-printing method
Meanwhile, Professor Il-Doo Kim was recently appointed as an Associate Editor of ACS Nano, a highly renowned journal in the field of nanoscience.
Professor Kim said, “It is my great honor to be an Associate Editor of the highly renowned journal ACS Nano, which has an impact factor reaching 13.709 with 134,596 citations as of 2017. Through the editorial activities in the fields of energy, I will dedicate myself to improving the prominence of KAIST and expanding the scope of Korea’s science and technology. I will also contribute to carrying out more international collaborations with world-leading research groups.”
(Associate Editor of ACS Nano Professor Il-Doo Kim)
2018.12.20 View 9317 -
Highly Scalable Process to Obtain Stable 2D Nanosheet Dispersion
(Professor Do Hyun Kim and his team)
A KAIST team developed technology that allows the mass production of two-dimensional (2D) nanomaterial dispersion by utilizing the characteristic shearing force of hydraulic power.
The 2D nanosheet dispersion can be directly applied to solution-based processes to manufacture devices for electronics as well as energy storage and conversion. It is expected to be used in these devices with improved performance.
There have been numerous researches on the mass production of various 2D nanomaterial because they show outstanding physical and chemical characteristics when they are truly 2D.
With strong mechanical force or chemical reaction only, each existing exfoliation method has its limitation to make 2D material when the scale of manufacturing increases. They also face the issues of high cost and long process time.
Moreover, 2D nanosheets by the exfoliation have the tendency of agglomeration due to the surface energy. Usually, organic solvent or surfactant is required to obtain high yield and concentration of 2D material by minimizing agglomeration.
After several years of research, Professor Do Hyun Kim in the Department of Chemical and Biomolecular Engineering and his team verified that optimized shearing in their reactor provided the highest efficiency for the exfoliation of nanomaterial. For the increased reactor capacity, they selected a flow and a dispersive agent to develop a high-speed, mass-production process to get 2D nanosheets by physical exfoliation with an aqueous solution.
The team proposed a flow reactor based on Taylor-Couette flow, which has the advantage of high shear rate and mixing efficiency even under large reactor capacity.
In this research, Professor Young-Kyu Han at Dongguk University-Seoul carried out the Ab initio calculation to select the dispersive agent. According to his calculation, an ionic liquid can stabilize and disperse 2D nanomaterial even in a small concentration. This calculation could maximize the exfoliating efficiency.
Professor Bong Gill Choi at Kangwon National University carried out the evaluation of device made of resulting dispersion. The team used a membrane filtration process to make a flexible and highly conductive film of 2D material. The film was then applied to produce an electrode for the supercapacitor device with very high capacity per volume. They also confirmed its stability in their supercapacitor device.
Additionally, they applied dispersive nanomaterials including graphene, molybdenum disulfide (MoS₂), and boron nitride (BN) to inkjet printer ink and realized micrometer-thick nanomaterial patterns on A4 paper. The graphene ink showed no loss of electrical property after printing without additional heat treatment.
Professor Kim said, “This new technology for the high-speed mass production of nanomaterials can easily be applied to various 2D nanomaterials. It will accelerate the production of highly efficient devices for optoelectronics, biosensors, and energy storage/conversion units with low cost.”
This research, led by Dr. Jae-Min Jeong, was published in Advanced Functional Materials on August 12.
Figure 1. The cover page of Advanced Functional Materials
2018.12.19 View 5235 -
Optimal Immuno-Therapeutic Strategies for Liver Cancer
KAIST medical scientists have presented a heterogeneity of immune cell exhaustion in the cancer environment, providing evidence and rationale for designing optimal strategies for immune checkpoint inhibitors in liver cancer patients.
They succeeded in distinguishing the hepatocellular carcinoma group from the exhausted tumor infiltrating immune cell composition of liver cancer patients. The study, conducted in collaboration with Asan Medical Center, confirmed the applicability for liver cancer patients, providing a new path for personalized precision medicine as well as a new model for translational research.
Our immune system is able to destroy cancerous cells in our body, however sometimes cancer cells can adapt and mutate, effectively hiding from our immune system. One of the mechanisms that has evolved to prevent eradication by the immune system is to functionally silence effector T cells, termed T-cell exhaustion, that is mainly mediated by immune checkpoint molecules such as PD-1, TIM-3, and LAG-3.
Recent breakthroughs and encouraging clinical results with various immune checkpoint inhibitors (ICIs), such as anti-PD-1 monoclonal antibodies (mAbs) and anti-CTLA-4 mAbs, have demonstrated tremendous potential to cure cancers through the immune activation of exhausted T cells. Immune checkpoint inhibitors showed significant clinical benefits for several types of cancers, leading to their wide application in clinical practice.
Anti-PD1 blocking antibodies are one of the most representative agents in this class of drug. However, it has been challenging to precisely understand the biological and clinical significance of T-cell exhaustion in cancer. A KAIST research team led by Professor Su-Hyung Park reported the heterogeneity of T-cell exhaustion in hepatocellular carcinoma (HCC) and its potential clinical implications in Gastroenterology on December 4.
The team revealed that heterogeneous T-cell exhaustion status is determined by the differential PD-1 expression levels in CD8+ T cells in liver cancer patients. The authors found that tumor-infiltrating CD8+ T cells with high PD-1 expression from liver cancer patients are functionally impaired and co-express other immune checkpoint receptors such as TIM-3 and/or LAG3, compared to those with low PD-1 expression.
Moreover, based on these results, the authors suggested that liver cancer patients can be classified into two distinct subgroups. Patients having high PD-1 expression levels in the tumor microenvironment showed more aggressive tumor features and biomarkers predicting a favorable response to anti-PD1 therapy. The research team also demonstrated that only liver cancer patients having high PD-1 expression are susceptible to combined immune checkpoint blockade-based therapies.
Prof. Park said, “The new classification of liver cancer patients identified by this study can be utilized as a biomarker to predict the response of current cancer immunotherapy targeting the PD-1 pathway.” He also said they will continue to conduct research on T-cell exhaustion and activation in various types of cancer, which could lead to a better understanding of T-cell response against cancer, thereby providing evidence for future cancer immunotherapy to achieve the ultimate goal to prolong the survival of cancer patients.
2018.12.18 View 4486 -
Characteristics of Submesoscale Geophysical Turbulence Reported
A KAIST research team has reported some of unique characteristics and driving forces behind submesoscale geophysical turbulence. Using big data analysis on ocean surface currents and chlorophyll concentrations observed using coastal radars and satellites has brought better understanding of oceanic processes in space and time scales of O(1) kilometer and O(1) hour. The outcomes of this work will lead to improved tracking of water-borne materials and performance in global and regional climate prediction models.
In 2012, United States National Aeronautics and Space Administration (NASA) released a movie clip called “Perpetual Oceans”, which visualized ocean circulation obtained from satellite altimeter-derived sea surface height observations over two and a half years. When the movie was released to the public, it received a great deal of attention because the circulation patterns were strikingly similar to “The Starry Night” by Vincent van Gogh.
“Perpetual Oceans” is full of vortical flow patterns describing the oceanic turbulent motions at mesoscale (a scale of 100 km or larger). Meanwhile, Professor Sung Yong Kim from the Department of Mechanical Engineering and his team focused on the study of the oceanic turbulence at sub-mesoscale (space and time scales of 1 to 100 km and hours).
Sub-mesoscale processes are important because they contribute to the vertical transport of oceanic tracers, mass, buoyancy, and nutrients and rectify both the mixed layer structure and upper ocean stratification. These process studies have been primarily based on numerical simulations because traditional in situ ocean measurements can be limited in their capability to resolve the detailed horizontal and vertical structures of these processes.
The team conducted big data analysis on hourly observations of one-year ocean surface current maps and five-year chlorophyll concentration maps, obtained from remote sensing instruments such as coastal high-frequency radars (HFRs) and geostationary ocean color imagery (GOCI) to examine the unique characteristics of oceanic submesoscale processes.
The team analyzed the slope change of the wavenumber energy spectra of the observations in terms of season and sampling directions. Through the analysis, the team proved that energy cascade (a phenomenon in which large-scale energy transfers to small-scale energy or vice-versa during the turbulent energy transit) occurs in the spatial scale of 10 km in the forward and inverse directions. This is driven by baroclinic instability as opposed to the mesoscale eddy-driven frontogenesis at the O(100) km scale based on the observed regional submesoscale circulations.
This work will contribute to the parameterization of physical phenomenon of sub-mesoscale in the field of global high-resolution modeling within ocean physics and atmospheric as well as climate change. Based on the understanding of the principle of sub-mesoscale surface circulation, practical applications can be further derived for radioactivity, oil spill recovery, and marine pollutant tracking.
Moreover, the data used in this research was based on long-term observations on sub-mesoscale surface currents and concentrations of chlorophyll, which may reflect the submesoscale processes actively generated in the subpolar front off the east coast of Korea. Hence, this study can potentially be beneficial for integrated big data analyses using high-resolution coastal radar-derived surface currents and satellite-derived products and motivate interdisciplinary research between ocean physics and biology.
This research was published as two companion papers in the Journal of Geophysical Research: Oceans on August 6, 2018. (doi:10.1002/2016JC012517; doi:10.1002/2017JC013732)
Figure 1.'The Starry Night' of Van Gogh and the 'Perpetual Ocean' created by NASA's Goddard Space Flight Center.
Figure 2. A schematic diagram of the energy cascades in forward and backward directions and the spatial scale where the energy is injected.
Figure 3. A snapshot of the chlorophyll concentration map derived from geostationary ocean color imagery (GOCI) off the east coast of Korea presenting several examples of sub-mesoscale turbulent flows.
Figure 4. Energy spectra of the HFR-derived surface currents and GOCI-derived chlorophyll concentrations and the temporal variability of spectral decay slopes in the cross-shore and along-shore directions.
2018.12.13 View 4803 -
AI-based Digital Watermarking to Beat Fake News
(from left: PhD candidates Ji-Hyeon Kang, Seungmin Mun, Sangkeun Ji and Professor Heung-Kyu Lee)
The illegal use of images has been a prevalent issue along with the rise of distributing fake news, which all create social and economic problems. Here, a KAIST team succeeded in embedding and detecting digital watermarks based on deep neural learning artificial intelligence, which adaptively responds to a variety of attack types, such as removing watermarks and hacking. Their research shows that this technology reached a level of reliability for technology commercialization.
Conventional watermarking technologies show limitations in terms of practicality, technology scalability, and usefulness because they require a predetermined set of conditions, such as the attack type and intensity. They are designed and implemented in a way to satisfy specific conditions.
In addition to those limitations, the technology itself is vulnerable to security issues because upgraded hacking technologies are constantly emerging, such as watermark removal, copying, and substitution.
Professor Heung-Kyu Lee from the School of Computing and his team provided a web service that responds to new attacks through deep neural learning artificial intelligence. It also serves as a two-dimensional image watermarking technique based on neural networks with high security derived from the nonlinear characteristics of artificial neural networks. To protect images from varying viewpoints, the service offers a depth-image-based rendering (DIBR) three-dimensional image watermarking technique.
Lastly, they provided a stereoscopic three-dimensional (S3D) image watermarking technique that minimizes visual fatigue due to the embedded watermarks. Their two-dimensional image watermarking technology is the first of its kind to be based upon artificial neural works. It acquires robustness through educating the artificial neural networking on various attack scenarios.
At the same time, the team has greatly improved on existing security vulnerabilities by acquiring high security against watermark hacking through the deep structure of artificial neural networks. They have also developed a watermarking technique embedded whenever needed to provide proof during possible disagreements.
Users can upload their images to the web service and insert the watermarks. When necessary, they can detect the watermarks for proof in any dispute.
Moreover, this technology provides services, including simulation tools, watermark adjustment, and image quality comparisons before and after the watermark is embedded.
This study maximized the usefulness of watermarking technology by facilitating additional editing and demonstrating robustness against hacking.
Hence, this technology can be applied in a variety of contents for certification, authentication, distinction tracking, and copyrights. It can contribute to spurring the content industry and promoting a digital society by reducing the socio-economic losses caused by the use of various illegal image materials in the future.
Professor Lee said, “Disputes related to images are now beyond the conventional realm of copyrights. Recently, their interest has rapidly expanded due to the issues of authentication, certification, integrity inspection, and distribution tracking because of the fake video problem. We will lead digital watermarking research that can overcome the technical limitations of conventional watermarking techniques.”
This technology has only been conducted in labs thus far, but it is now open to the public after years of study. His team has been conducting a test run on the webpage (click).Moving forward from testing the technology under specific lab conditions, it will be applied to a real environment setting where constant changes pervade.
1. Figure. 2D image using the watermarking technique: a) original image b) watermark-embedded image c) signal from the embedded watermark
Figure 2. Result of watermark detection according to the password
Figure 3. Example of a center image using the DIBR 3D image watermarking technique: a) original image b) depth image c) watermark-embedded image d) signal from the embedded watermark
Figure 4. Example of using the S3D image watermarking technique: a) original left image b) original right image c) watermark-embedded left image d) watermark-embedded right image e) signal from the embedded watermark (left) f) signal from the embedded watermark (right)
2018.12.05 View 4593 -
Reducing the Drag Force of a Moving Body Underwater
(from left: Professor Yeunwoo Cho and PhD Jaeho Chung)
Professor Yeunwoo Cho and his team from the Department of Mechanical Engineering developed new technology that reduces the drag force of a moving body in a still fluid by using the supercavitation phenomenon.
When a body moves in air, the frictional drag is lower than that of the same body moving in water. Therefore, the body that moves in water can reduce the drag significantly when it is completely enveloped in a gaseous cavity.
The team used compressed air to create so-called supercavitation, which is a phenomenon created by completely enveloping a body in a single large gaseous cavity. The drag force exerted on the body is then measured.
As a result, the team confirmed that the drag force for a moving body enveloped in air is about 25% of the drag force for a moving body without envelopment.
These results can be applied for developing high-speed underwater vehicles and the development of air-lubricated, high-speed vessels.
The team expects that the results can be applied for developing high-speed underwater vehicles and the development of air lubrication for a ship’s hull.
This research, led by PhD Jaeho Chung, was published in the Journal of Fluid Mechanics as a cover article on November 10, 2018.
Figure 1. The cover article of the Journal of Fluid Mechanics Vol. 854
2018.12.04 View 3722 -
From Concept to Reality: Changing Color of Light Using a Spatiotemporal Boundary
(from left: Professor Bumki Min, PhD candidate Jaehyeon Son and PhD Kanghee Lee)
A KAIST team developed an optical technique to change the color (frequency) of light using a spatiotemporal boundary. The research focuses on realizing a spatiotemporal boundary with a much higher degree of freedom than the results of previous studies by fabricating a thin metal structure on a semiconductor surface. Such a spatiotemporal boundary is expected to be applicable to an ultra-thin film type optical device capable of changing the color of light.
The optical frequency conversion device plays a key role in precision measurement and communication technology, and the device has been developed mainly based on optical nonlinearity.
If the intensity of light is very strong, the optical medium responds nonlinearly so the nonlinear optical phenomena, such as frequency doubling or frequency mixing, can be observed. Such optical nonlinear phenomena are realized usually by the interaction between a high-intensity laser and a nonlinear medium.
As an alternative method frequency conversion is observed by temporally modifying the optical properties of the medium through which light travels using an external stimulus. Since frequency conversion in this way can be observed even in weak light, such a technique could be particularly useful in communication technology.
However, rapid optical property modification of the medium by an external stimulus and subsequent light frequency conversion techniques have been researched only in the pertubative regime, and it has been difficult to realize these theoretical results in practical applications.
To realize such a conceptual idea, Professor Bumki Min from the Department of Mechanical Engineering and his team collaborated with Professor Wonju Jeon from the Department of Mechanical Engineering and Professor Fabian Rotermund from the Department of Physics. They developed an artificial optical material (metamaterial) by arranging a metal microstructure that mimics an atomic structure and succeeded in creating a spatiotemporal boundary by changing the optical property of the artificial material abruptly.
While previous studies only slightly modified the refractive index of the medium, this study provided a spatiotemporal boundary as a platform for freely designing and changing the spectral properties of the medium. Using this, the research team developed a device that can control the frequency of light to a large degree.
The research team said a spatiotemporal boundary, which was only conceptually considered in previous research and realized in the pertubative regime, was developed as a step that can be realized and applied.
Professor Min said, “The frequency conversion of light becomes designable and predictable, so our research could be applied in many optical applications. This research will present a new direction for time-variant media research projects in the field of optics.”
This research, led by PhD Kanghee Lee and PhD candidate Jaehyeon Son, was published online in Nature Photonics on October 8, 2018.
This work was supported by the National Research Foundation of Korea (NRF) through the government of Korea. The work was also supported by the Center for Advanced Meta-Materials (CAMM) funded by the Korea Government (MSIP) as the Global Frontier Project (NRF-2014M3A6B3063709).
Figure 1. The frequency conversion process of light using a spatiotemporal boundary.
Figure 2. The complex amplitude of light at the converted frequency with the variation of a spatiotemporal boundary.
2018.11.29 View 6893 -
Silk Adhesive Paves the Way for Epidermal Electronics
(from left: Dr. Ji-Won Seo, Professor Hyunjoo Jenny Lee and PhD candidate, Hyojung Kim)
Producing effective epidermal electronics requires a strong, biocompatible interface between a biological surface and a sensor. Here, a KAIST team employed a calcium-modified silk fibroin as a biocompatible and strong adhesive. This technology led to the development of epidermal electronics with strong adhesion for patients who need drug injections and physiological monitoring over a long time.
Recently, biocompatible silk fibroins has been increasingly used for flexible substrates and water-soluble sacrificial layers because they allow structural modifications and are biodegradable. From previous studies, the team discovered the adhesive properties of silk fibroin via metal chelate bonding and the water-capturing of Ca ions.
Professor Hyunjoo Jenny Lee from the School of Electrical Engineering and her team explored ways to develop reusable, water-degradable, biocompatible and conductive epidermal electronics that can be attached to the human skin for long-term use. To overcome the limitations of conventional silk fibroin, the team introduced Ca ions to modify silk fibroin into a strong and biocompatible adhesive.
Calcium ions adopted in silk fibroins serve to capture water and enhance the cohesion force through metal chelation. Therefore, this endows viscoelasticity to previously a firm silk fibroin. This modified silk fibroin exhibits strong viscoelasticity and strong adhesiveness when physically attached to the human skin and various polymer substrates. Their developed silk adhesive is reusable, water-degradable, biocompatible, and conductive.
To test the effectiveness, the team employed the silk adhesive to fabricate an epidermal capacitive touch sensor that can be attached to the human skin. They verified the reusability of the sensor by performing attachment and detachment tests. They also confirmed that the physical adhesion of the Ca-modified silk facilitates its reusability and possesses high peel strength.
Furthermore, they tested the stretchability of the silk adhesive on bladder tissue. Although it is not an epidermal skin, bladder tissue is highly stretchable. Hence, it is a perfect target to measure the resistance-strain characteristic of the silk adhesive. When the bladder tissue was stretched, the resistive strain epidermal sensor corresponded to the tensile strain.
Showing high biocompatibility, the silk adhesive is suitable for interfacing with the human skin for a long period of time. Therefore, it can also be applied to a drug delivery epidermal system as well as an electrocardiogram (ECG) epidermal sensor.
Professor Lee said, “We are opening up a novel use for silk by developing reusable and biodegradable silk adhesive using biocompatible silk fibroin. This technology will contribute to the development of next-generation epidermal electronics as well as drug delivery systems.
This research, led by Dr. Ji-Won Seo and a PhD candidate, Hyojung Kim, was published in Advanced Functional Materials on September 5, 2018.
Figure 1. Schematic and photograph of a hydrogel patch adhered on the human skin through the silk adhesive
Figure 2. Cover page of Advanced Functional Materials
2018.11.21 View 5790 -
Novel Strategies to Transform a Commercially Available Iboga Alkaloid to Post-Iboga Alkaloids
(PhD candidate HyeonggeunLim, Professor Sunkyu Han, PhD candidate Sikwang Seong)
KAIST chemists have synthesized seven different iboga and post-iboga natural products from commercially available catharanthine by mirroring nature’s biosynthetic post-modification of the iboga skeleton. They devised a novel strategy to biosynthesize the natural products via a series of selective and efficient oxidation and rearrangement reactions. This will serve as a stepping stone for developing therapeutic medications against cancer and narcotics addiction.
The research team, led by Professor Sunkyu Han, conceptualized and coined the term “Post-Iboga” alkaloids to describe the natural products that are biosynthetically derived from iboga-type alkaloids, which are composed of rearranged indole and/or isoquinuclidine backbones.
Iboga alkaloids have attracted significant attention from the scientific community due to their intriguing polycyclic structures and potential therapeutic uses against drug addictions. Nature has evolved to add architectural repertoires to this family of secondary metabolites by diversifying the iboga frameworks.
Notable examples are the FDA-approved anticancer drugs vinblastine and vincristine, both derived by the oxidative dimerization of catharanthine and vindoline subunits. Admittedly, synthetic foci toward the biosynthetic iboga-derivatives have historically been on these aforementioned dimeric natural products.
Recent natural product isolation studies on Tabernaemontana corymbosa and Ervatamia officinalis species have resulted in discoveries of various secondary metabolites that are biosynthetically derived from iboga alkaloids. These recent outbursts of iboga-derived natural product isolation reports have kindled interests toward these family of natural products.
The research team utilized (+)-catharanthine, the starting material for the industrial production of the anticancer drug Navelbine®. Well-orchestrated oxidations at the C19 position and the indole moiety of the catharanthine derivative, followed by differential rearrangements under acidic conditions, provided synthetic samples of voatinggine and tabertinggine respectively.
On the other hand, opportune oxidations at the C19 position and the alpha position of the tertiary amine moiety of the catharantine derivative, followed by a transhemiaminalization, produced the first synthetic sample of chippiine/dippinine-type natural product, dippinine B.
It is important to note that the chippiine and dippinine-type alkaloids have been targeted among synthetic chemists for over 30 years but had not succumbed to synthesis prior to this report.
Professor Han believes that their study will serve as a blueprint for further explorations of the synthesis, biosynthesis, and pharmacology of this emerging family of natural products. This study was published in Chem on November 15, 2018 (DOI: 10.1016/j.chempr.2018.10.009).
2018.11.16 View 4936 -
New Anisotropic Conductive Film for Ultra-Fine Pitch Assembly Applications
(Professor Paik(right) and PhD Candidate Yoon)
Higher resolution display electronic devices increasingly needs ultra-fine pitch assemblies. On that account, display driver interconnection technology has become a major challenge for upscaling display electronics.
Researchers have moved to one step closer to realizing ultra-fine resolution for displays with a novel thermoplastic anchoring polymer layer structure. This new structure can significantly improve the ultra-fine pitch interconnection by effectively suppressing the movement of conductive particles. This film is expected to be applied to various mobile devices, large-sized OLED panels, and VR, among others.
A research team under Professor Kyung-Wook Paik in the Department of Materials developed an anchoring polymer layer structure that can effectively suppress the movement of conductive particles during the bonding process of the anisotropic conductive films (ACFs). The new structure will significantly improve the conductive particle capture rate, addressing electrical short problems in the ultra-fine pitch assembly process.
During the ultra-fine pitch bonding process, the conductive particles of conventional ACFs agglomerate between bumps and cause electrical short circuits. To overcome the electrical shortage problem caused by the free movement of conductive particles, higher tensile strength anchoring polymer layers incorporated with conductive particles were introduced into the ACFs to effectively prevent conductive particle movement.
The team used nylon to produce a single layer film with well-distributed and incorporated conductive particles. The higher tensile strength of nylon completely suppressed the movement of conductive particles, raising the capture rate of conductive particles from 33% of the conventional ACFs to 90%. The nylon films showed no short circuit problem during the Chip on Glass assembly. Even more, they obtained excellent electrical conductivity, high reliability, and low cost ACFs during the ultra-fine pitch applications.
Professor Paik believes this new type of ACFs can further be applied not only to VR, 4K and 8K UHD display products, but also to large-size OLED panels and mobile devices.
His team completed a prototype of the film supported by the ‘H&S High-Tech,’ a domestic company and the ‘Innopolis Foundation.’ The study, whose first author is PhD candidate Dal-Jin Yoon, is described in the October issue of IEEE TCPMT.
Figure 1: Schematic process of APL structure fabrication.
Figure 2: Proto-type production of APL ACFs.
2018.11.13 View 5693 -
Faster and More Powerful Aqueous Hybrid Capacitor
(Professor Jeung Ku Kang from the Graduate School of EEWS)
A KAIST research team made it one step closer to realizing safe energy storage with high energy density, high power density, and a longer cycle life. This hybrid storage alternative shows power density 100 times faster than conventional batteries, allowing it to be charged within a few seconds. Hence, it is suitable for small portable electronic devices.
Conventional electrochemical energy storage systems, including lithium-ion batteries (LIBs), have a high voltage range and energy density, but are subject to safety issues raised by flammable organic electrolytes, which are used to ensure the beneficial properties. Additionally, they suffer from slow electrochemical reaction rates, which lead to a poor charging rate and low power density with a capacity that fades quickly, resulting in a short cycle life.
On the other hand, capacitors based on aqueous electrolytes are receiving a great deal of attention because they are considered to be safe and environmentally friendly alternatives. However, aqueous electrolytes lag behind energy storage systems based on organic electrolytes in terms of energy density due to their limited voltage range and low capacitance.
Hence, developing aqueous energy storage with high energy density and a long cycle life in addition to the high power density that enables fast charging is the most challenging task for advancing next-generation electrochemical energy storage devices.
Here, Professor Jeung Ku Kang from the Graduate School of Energy, Environment, Water and Sustainability and his team developed an aqueous hybrid capacitor (AHC) that boasts high energy density, high power, and excellent cycle stability by synthesizing two types of porous metal oxide nanoclusters on graphene to create positive and negative electrodes for AHCs.
The porous metal oxide nanoparticles are composed of nanoclusters as small as two to three nanometers and have mesopores that are smaller than five nanometers. In these porous structures, ions can be rapidly transferred to the material surfaces and a large number of ions can be stored inside the metal oxide particles very quickly due to their small particle size and large surface area.
The team applied porous manganese oxide on graphene for positive electrodes and porous iron oxide on graphene for negative electrodes to design an aqueous hybrid capacitor that can operate at an extended voltage range of 2V.
Professor Kang said, “This newly developed AHC with high capacity and power density driven from porous metal oxide electrodes will contribute to commercializing a new type of energy storage system. This technology allows ultra-fast charging within several seconds, making it suitable as a power source for mobile devices or electric vehicles where solar energy is directly stored as electricity.”
This research, co-led by Professor Hyung Mo Jeong from Kangwon National University, was published in Advanced Functional Materials on August 15, 2018.
Figure 1. Image that shows properties of porous metal oxide nanoparticles formed on graphene in the aqueous hybrid capacitor
2018.11.09 View 6671 -
Controlling Crystal Size of Organic Semiconductors
A KAIST research team led by Professor Steve Park from the Department of Materials Science and Engineering
Recently, solution-processable organic semiconductors are being highlighted for their potential application in printed electronics, becoming a feasible technique to fabricate large-area flexible thin film at a low cost. The field-effect mobility of small-molecule organic semiconductors is dependent on the crystallinity, crystal orientation, and crystal size. A variety of solution-based coating techniques, such as ink-jet printing, dip-coating, and solution shearing have been developed to control the crystallinity and crystal orientation, but a method for developing techniques to increase the crystal size of organic semiconductors is still needed.
To overcome this issue, the research team developed an inorganic polymer micropillar-based solution shearing system to increase the crystal size of an organic semiconductor with pillar size. Using this technique, the crystallization process of organic semiconductors can be controlled precisely, and therefore large-area organic semiconductor thin film with controlled crystallinity can be fabricated.
A variety of solution-based coating techniques cannot control the fluid-flow of solutions appropriately, so the solvent evaporates randomly onto the substrate, which has difficulty in the fabrication of organic semiconductor thin film with a large crystal size.
The research team integrated inorganic polymer microstructures into the solution shearing blade to solve this issue. The inorganic polymer can easily be microstructured via conventional molding techniques, has high mechanical durability, and organic solvent resistance. Using the inorganic polymer-based microstructure blade, the research team controlled the size of small molecule organic semiconductors by tuning the shape and dimensions of the microstructure. The microstructures in the blade induce the sharp curvature regions in the meniscus line that formed between the shearing blade and the substrate, and therefore nucleation and crystal growth can be regulated. Hence, the research team fabricated organic semiconductor thin-film with large crystals, which increases the field-effect mobility.
The research team also demonstrated a solution shearing process on a curved surface by using a flexible inorganic polymer-based shearing blade, which expands the applicability of solution shearing.
Professor Park said, “Our new solution shearing system can control the crystallization process precisely during solvent evaporation.” He added, “This technique adds another key parameter that can be utilized to tune the property of thin films and opens up a wide variety of new applications.
The results of this work entitled “Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size” was published in the July 2018 issue of Advanced Materials as a cover article.
2018.10.30 View 5306