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23 results on '"Gu, Kaichen"'

1. Using 4D STEM to probe mesoscale order in molecular glass films prepared by physical vapor deposition

Author

Chatterjee, Debaditya, Huang, Shuoyuan, Gu, Kaichen, Ju, Jianzhu, Yu, Junguang, Bock, Harald, Yu, Lian, Ediger, M. D., and Voyles, Paul M.

Subjects
Condensed Matter - Materials Science
Abstract

Physical vapor deposition can be used to prepare highly stable organic glass systems where the molecules show orientational and translational ordering at the nanoscale. We have used low-dose four-dimensional scanning transmission electron microscopy (4D STEM), enabled by a fast direct electron detector, to map columnar order in glassy samples of a discotic mesogen using a 2 nm probe. Both vapor deposited and liquid cooled glassy films show domains of similar orientation, but their size varies from tens to hundreds of nanometers, depending on processing. Domain sizes are consistent with surface diffusion mediated ordering during film deposition. These results demonstrate the ability of low-dose 4D STEM to characterize mesoscale structure in a molecular glass system which may be relevant to organic electronics.

Published
2023
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2. Epitaxially crystallized polyethylene exhibiting near-equilibrium melting temperatures

Author

Wang, Yucheng, Liu, Jason X., Gu, Kaichen, Soman, Anishkumar, Gu, Tingyi, Arnold, Craig B., Register, Richard A., Loo, Yueh-Lin, and Priestley, Rodney D.

Subjects
Crystallization -- Research, Polyethylene -- Chemical properties -- Thermal properties, Chemical research, Engineering and manufacturing industries, Science and technology
Abstract

The morphology and orientation of polymer crystals are important factors which determine the performance of thin-film, polymer-based technologies such as organic electronic devices and gas separation membranes. Here, we utilize polymer-substrate epitaxy to achieve a highly oriented crystalline morphology during thin-film processing. To accomplish this, we employ matrixassisted pulsed laser evaporation (MAPLE), a slow physical vapor deposition process, to deposit linear polyethylene epitaxially atop a graphene substrate. Via MAPLE, we demonstrate the ability to achieve a film morphology comprised of well-aligned, edge-on crystalline lamellae. Furthermore, we show that MAPLE can be exploited to grow crystalline lamellae composed entirely of extended polymer chains which exhibit a near-equilibrium melting temperature. Our study demonstrates that MAPLE, as a bottom-up approach, can deposit polymer thin films with improved control over crystalline morphology. KEYWORDS epitaxial polymer crystallization, graphene, grazing-incidence x-ray diffraction, matrixassisted pulsed laser evaporation, melting, 1 | INTRODUCTION Enforcing the crystallization of polymers into a desired thin-film morphology remains a major scientific challenge. [4] Yet, the morphology is a critical factor determining the performance of [...]

Published
2022
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7. Computationally aided design of a high-performance organic semiconductor: the development of a universal crystal engineering core† †Electronic supplementary information (ESI) available: Synthetic details, characterization of synthesized materials, absorption spectra, and additional information on computational details and device fabrication. CCDC 1833615–1833619 and 1922871–1922873. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9sc02930c

Author

Petty, Anthony J., Ai, Qianxiang, Sorli, Jeni C., Haneef, Hamna F., Purdum, Geoffrey E., Boehm, Alex, Granger, Devin B., Gu, Kaichen, Rubinger, Carla Patricia Lacerda, Parkin, Sean R., Graham, Kenneth R., Jurchescu, Oana D., Loo, Yueh-Lin, Risko, Chad, and Anthony, John E.

Subjects
Chemistry
Abstract

Silylethyne-functionalized benzodithiophene serves as a universal crystal engineering core to yield stable, soluble, π-stacked arrays of aromatic chromophores., Herein, we describe the design and synthesis of a suite of molecules based on a benzodithiophene “universal crystal engineering core”. After computationally screening derivatives, a trialkylsilylethyne-based crystal engineering strategy was employed to tailor the crystal packing for use as the active material in an organic field-effect transistor. Electronic structure calculations were undertaken to reveal derivatives that exhibit exceptional potential for high-efficiency hole transport. The promising theoretical properties are reflected in the preliminary device results, with the computationally optimized material showing simple solution processing, enhanced stability, and a maximum hole mobility of 1.6 cm2 V–1 s–1.

Published
2019

8. Ultrathin and Ultrasensitive Direct X‐ray Detector Based on Heterojunction Phototransistors

Author

Gao, Yuanhong, primary, Ge, Yongshuai, additional, Wang, Xinwei, additional, Liu, Jin, additional, Liu, Wenquan, additional, Cao, Yong, additional, Gu, Kaichen, additional, Guo, Zheng, additional, Wei, Yu‐Ming, additional, Zhou, Ni, additional, Yu, De, additional, Meng, Hong, additional, Yu, Xue‐Feng, additional, Zheng, Hairong, additional, Huang, Wei, additional, and Li, Jia, additional

Published
2021
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16. Tunable properties of MAPLE-Deposited thin films in the presence of suppressed segmental dynamics

Author

Wang, Yucheng, Gu, Kaichen, Monnier, Xavier, Chowdhury, Mithun, Cangialosi, Daniele, Loo, Yueh-Lin, Priestley, Rodney D., Wang, Yucheng, Gu, Kaichen, Monnier, Xavier, Chowdhury, Mithun, Cangialosi, Daniele, Loo, Yueh-Lin, and Priestley, Rodney D.

Abstract

Processing polymer thin films by physical vapor deposition has been a major challenge due to material degradation. This challenge has limited our understanding of morphological control by top-down approaches that can be crucial for many applications. Recently, matrix-assisted pulsed laser evaporation (MAPLE) has emerged as an alternative route to fabricate polymer thin films from near-gas phase growth conditions. In this Letter, we investigate how this approach can result in a stable two-phase film structure of semicrystalline polymers via a unique combination of MAPLE and flash calorimetry. In the case of MAPLE-deposited poly(ethylene oxide) (PEO) thin films, we find a 35 °C enhancement in the glass transition temperature relative to melt-crystallized films, which is associated with irreversible chain adsorption in the amorphous region of the film. Remarkably, by varying substrate temperature during deposition, we reveal the ability to significantly tune the crystal orientation, extent of crystallinity, and lamellar thickness of MAPLE-deposited PEO thin films.

Published
2019

23. [Distribution of 21 organic ophospesters and their metabolites in drinking water in Dongcheng District of Beijing and their health hazard assessment in 2023].

Author

Yuan R, Tong J, Ding W, Huang L, Gu K, Cui X, and Fan S

Subjects
Humans, Adult, Female, Male, Risk Assessment, Beijing, Organophosphates analysis, Environmental Exposure adverse effects, Environmental Exposure analysis, Tandem Mass Spectrometry methods, Environmental Monitoring methods, Drinking Water chemistry, Drinking Water analysis, Esters analysis, Water Pollutants, Chemical analysis
Abstract

Objective: To investigate the pollution of organophosphate esters(OPEs) and their metabolites in drinking water in Dongcheng District of Beijing, and to assess the exposure risk of adults in drinking water., Methods: The contents of 14 OPEs and 7 metabolites in drinking water were determined by automatic solid phase extraction, isotope dilution and liquid chromatography tandem mass spectrometry. The average daily potential dose(ADD) were calculated based on the recommended intake of drinking water., Results: Seventeen pieces of tap water and 30 pieces of packaged drinking water collected by supermarket were measured. OPEs and di-OPEs were widely detected in drinking water(11 kinds of OPEs and 6 kinds of di-OPEs with the detection rate of more than 50%). The ΣOPEs range was 16.8 to 177ng/L, and the Σdi-OPEs range was 0.328 to 16.3 ng/L. The average daily dose of adult population was calculated: the ADD of 14 kinds of ΣOPEs in male and female were 3.15 and 3.10 ng/(kg·BW·d), and the P95 exposure was 6.95 and 7.00 ng/(kg·BW·d), respectively. The ADD of the seven Σdi-OPEs in male and female were 0.150 and 0.147 ng/(kg·BW·d), and the P95 exposure was 0.330 and 0.332 ng/(kg·BW·d), respectively. The hazard quotient(HQ) of exposure to OPEs through drinking water, calculated using the EPA's oral reference dose assessment, was much less than 1., Conclusion: The current exposure of OPEs via drinking water poses a low health risk to adult residents in Dongcheng District. However, due to the lack of Health-based guidance values for the metabolites of OPEs, the exposure risk may be underestimated.

Published
2024
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