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RISS 인기검색어
- 검색키워드
- 저자 : Seoncheol Cha (검색결과 4 건)
- 무료
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- 유료
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Structures of ionic liquid–water mixtures investigated by IR and NMR spectroscopy
Cha, Seoncheol,Ao, Mingqi,Sung, Woongmo,Moon, Bongjin,Ahlströ,m, Bodil,Johansson, Patrik,Ouchi, Yukio,Kim, Doseok The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.20
<P>Imidazolium-based ionic liquids having different anions 1-butyl-3-methylimidazolium ([BMIM]X: X = Cl<SUP>−</SUP>, Br<SUP>−</SUP>, I<SUP>−</SUP>, and BF<SUB>4</SUB><SUP>−</SUP>) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. The IR spectra of these ionic liquids in the CH<SUB><I>x</I></SUB> stretching region differed substantially, especially for C–H bonds in the imidazolium ring, and the NMR chemical shifts of protons in the imidazolium ring also varied markedly for ILs having different anions. Upon the introduction of water to screen the electrostatic forces and separate the ions, both IR and NMR spectra of [BMIM]X (X = Cl<SUP>−</SUP>, Br<SUP>−</SUP>, I<SUP>−</SUP>) showed significant changes, while those of [BMIM]BF<SUB>4</SUB> did not change appreciably. H–D isotopic exchange rates of C(2)–H in [BMIM]X–D<SUB>2</SUB>O mixtures exhibited an order: C(2)–H⋯Cl > C(2)–H⋯Br > C(2)–H⋯I, while the C(2)–H of [BMIM]BF<SUB>4</SUB> was not deuterated at all. These experimental findings, supported by DFT calculations, lead to the microscopic bulk configurations in which the anions and the protons of the cations in the halide ionic liquids have specific, hydrogen-bond type of interaction, while the BF<SUB>4</SUB><SUP>−</SUP> anion does not participate in the specific interaction, but interacts less specifically by positioning itself more above the ring plane of the imidazolium cation. This structural change dictated by the anion type will work as a key element to build the structure–property relationship of ionic liquids.</P> <P>Graphic Abstract</P><P>Imidazolium-based ionic liquids having different anions 1-butyl-3-methylimidazolium ([BMIM]X: X = Cl<SUP>−</SUP>, Br<SUP>−</SUP>, I<SUP>−</SUP>, and BF<SUB>4</SUB><SUP>−</SUP>) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00589a'> </P>
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Fluorescence Correlation Spectroscopy Study on Room-temperature Ionic Liquids
Seoncheol Cha,김도석 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.9
Unique fluorescence behavior was reported in room-temperature ionic liquids having imidazolium anion. Due to the molecular electronic energy level of imidazolium anion, fluorescence in the visible range from pure ionic liquids is not expected, but was readily observed. Fluorescence correlation spectroscopy (FCS) was used to find out the nature of this unique fluorescence by investigating the fluorescence fluctuation and the number density of fluorophores. FCS signal was observed in pure room-temperature ionic liquids having different cations and anions, which is considered to come from the molecular aggregate of room-temperature ionic liquid. The size and number density of aggregates in pure ionic liquids were measured by using FCS.
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Anion exchange in ionic liquid mixtures
Cha, Seoncheol,Kim, Doseok The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.44
<P>Advantage of ionic liquids as designer solvents can be maximized by mixing different ionic liquids (ILs) for a possibility of continuous tunability of material properties. The property of these mixed ILs would be determined by their microscopic conformation between cations and anions. The mixtures of two ILs having 1-butyl-3-methylimidaolium cations and different anions were investigated by IR and NMR spectroscopy, utilizing that the vibrational frequencies of the C–H stretching and bending modes of the most acidic proton in the imidazolium ring of the cation and the NMR chemical shift for the corresponding proton were clearly distinct between the ILs having different anions. The IR absorption spectra of the IL mixtures at different concentrations were well-matched to weighted sums of the two spectra of the pure ILs. In contrast, the two distinct peaks in the NMR spectra of the pure ILs coalesced into a single peak, which shifted continuously following the relative portion of two different ILs in the mixture. IR spectroscopy in the optical frequency range seems to take the instantaneous snapshot of the cation–anion interaction, while NMR spectroscopy in the radio-frequency (∼500 MHz) range samples over a much longer timescale, enough for the cation to interact with different anion species in the mixture.</P> <P>Graphic Abstract</P><P>Anion exchange in ionic liquid mixtures measured by IR and NMR spectroscopy. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp04276c'> </P>
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Viscosity of Sucrose Aqueous Solutions Measured by Using Fluorescence Correlation Spectroscopy
김도석,Seoncheol Cha,Sung Hyun Kim 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.4
Fluorescence correlation spectroscopy (FCS) is a technique for investigating diffusion phenomena from fluorescence fluctuation in a small volume. As the diffusion coefficient of fluorescent dye is governed by the properties of surrounding liquids, essential properties, such as the viscosity can be measured by using FCS, provided enough care is taken to account for subtle changes in the experimental conditions. We characterized the performance of FCS as a micro-viscometer by monitoring the diffusional motion of dye molecules in aqueous sucrose solutions. The viscosity values of the sucrose solutions determined by using the Stokes-Einstein relations were reliable, and their variations under different experimental conditions, such as excitation beam power and data acquisition scheme, could be clarified, demonstrating that FCS is an suitable tool for determining the viscosity of liquid systems.
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