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- 저자 : SARKARSOURAV (검색결과 5 건)
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Sarkar, Sourav,Kim, Byungki Applied Science Publishers 2017 Polymer degradation and stability Vol.138 No.-
<P><B>Abstract</B></P> <P>A new series of urea-formaldehyde polymer microcapsules with two-component cores have been synthesized by an in-situ polymerization procedure. Graphene was used as one of the components in the core material along with a bisphenol-A epoxy resin. Preparation of graphene oxide was carried out by the Staudenmaier oxidation process, followed by further thermal treatment in a controlled environment to produce thermally treated graphene (TTG). The thermal and physical properties of the microcapsules were investigated by TGA (Thermogravimetric analysis) and, SEM (Scanning electron microscopy) among other methods. The chemical composition of the microcapsules was ascertained by FTIR (Fourier-transform infrared) spectroscopy. The resultant graphene-encapsulated microcapsules have shown an increasing degree of thermal stability in the range from 250 °C to over 400 °C, depending on the TTG wt%. They also exhibited good storage stability (>90%) over different periods of time. It was determined that the thermal and physical properties of the microcapsules are closely linked to the core materials and the processing conditions. The processing conditions, in turn, can be varied to synthesize different types of microcapsules with different sizes, thermal stability and yield percentage values. The improved sway over the thermal degradation provided better control over the release rate of the core material under various conditions. Also, the unusually high thermal stability behavior of the polymer microcapsules' shell wall demonstrates better survivability of these microcapsules under harsh external conditions which can be exploited in their use as highly stable self-healing agent carrier in high-performance polymer materials.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Sarkar, Sourav,Santra, Mithun,Singha, Subhankar,Jun, Yong Woong,Reo, Ye Jin,Kim, Hye Rim,Ahn, Kyo Han The Royal Society of Chemistry 2018 Journal of Materials Chemistry B Vol.6 No.27
<P>Fluorescent compounds with distinct photophysical properties are essential for the development of optical probes for chemical, biological, and environmental species, in addition to optoelectronic devices. In this context, we synthesized a series of 3-substituted-8-hydroxybenzo[<I>g</I>]coumarin derivatives and characterized their photophysical and cellular imaging properties. Being dipolar π-extended coumarin analogues, they have intramolecular charge-transfer character and good two-photon imaging capability, as shown for two selected dyes. Most of the dyes emit in a wavelength range of 530-580 nm in aqueous media and show large Stokes shifts as high as 197 nm. In spite of its dipolar nature, the 3-pyridinium-substituted derivative 5h notably shows insignificant solvatochromism as well as viscosity- and polarity-insensitive emission intensity, offering an ideal dye platform for probing biological targets. As a demonstration, we prepared an esterase probe based on it, which shows ratiometric sensing behavior.</P>
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Graphene-Based Composite Protective Coating for Twisted Strings and Its Experimental Evaluation
Sarkar, Sourav,Ishfaque, Asif,Usman, Muhammad,Gaponov, Igor,Kim, Byungki IEEE 2018 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. No.
<P>Twisted string actuators (TSAs) have found extensive use in various areas of engineering and in consumer products due to their mechanical simplicity and flexibility. Despite huge future potential of TSAs, reliability of the strings operating in stringent conditions has remained a significant concern. The increased string wear due to friction between the fibers and strands is the main reason of comparatively short lifetime of the strings in TSAs. However, very limited research has been done in this area, thus methods to extend the string lifetime remains an open question. Similarly, despite intensive research efforts on graphene over the past decade, its potential as reinforcement in coating material remains comparatively unexplored. In this paper, we report the preparation and implementation of a unique graphene-based composite coating for TSAs. The graphene sample was analyzed by both structural and chemical characterization procedures before the preparation of the coating material. The coated strings were also analyzed thoroughly using both spectroscopic and microscopic techniques. The experimental studies demonstrated that we could increase lifetime of the newly coated strings by approximately 100 <TEX>$\%$</TEX> in comparison with the coated strings procured commercially. The development of this new graphene-based coating material may usher a favorable outlook in the application of TSAs in future.</P>
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Seo Won Cho,노예진,SARKARSOURAV,Kyo Han Ahn 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.1
The palladium catalyzed cross-coupling reactions are indispensable in organic synthesis of pharmaceutical compounds, demanding convenient tools for the analysis of residual palladium contents. Propargyl aryl ether-type fluorescent sensing systems that detect Pd(0)/Pd(II)/Pd(IV) species through depropargylation require no additives. We investigated a ratiometric sensing system based on a benzocoumarin dye; thus, three propargyl aryl ethers bearing electronically-different self-immolative linkers were synthesized and their relative response rate toward Pd(0) and Pd(II) were compared. We found that the response rate became faster when the self-immolative linker became more electron-deficient. The best-performing system sensed Pd(0)/Pd(II) species selectively against various other metal species, which is also capable of fluorescent imaging of Pd(0)/Pd(II) species in cells. The work provides us a clue to accelerate the catalytic depropargylation step, which, when combined with a novel fluorophore, would enable us to develop out-performing palladium sensing systems.
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